Dental compositions including a thermally labile component, and the use thereof

ABSTRACT

Hardenable and hardened dental compositions, and articles including such hardenable and hardened compositions, are provided. The hardenable dental compositions include a thermally labile component including one or more thermally labile groups. Upon heating, the hardened compositions are useful, for example, for reducing the bond strength of orthodontic appliances adhered to tooth structures with the hardened compositions.

BACKGROUND

Orthodontic treatment involves movement of malpositioned teeth toorthodontically correct positions. Tiny orthodontic appliances known asbrackets are connected to exterior surfaces of the patient's teeth, andan archwire is placed in a slot of each bracket. The archwire forms atrack to guide movement of the teeth to desired positions for correctocclusion. End sections of the archwire are often received in appliancesknown as buccal tubes that are fixed to the patient's molar teeth. Inrecent years it has become common practice to use adhesives to bondorthodontic appliances to the surface of the tooth, using either director indirect methods. A variety of adhesives are available to thepractitioner for bonding brackets to tooth surfaces, and many offerexcellent bond strengths. High bond strengths are desirable formaintaining adhesion of the bracket to the tooth surface over theduration of the treatment process, which can typically be two years ormore.

However, orthodontic adhesives with high bond strengths can lead toother difficulties. For example, one of the most difficult aspects ofthe orthodontic treatment process can be the removal of the bracketafter completion of treatment. It is well known in the industry thatcertain adhesives, used in combination with certain rigid brackets, arecapable of causing enamel fracture under some debonding conditions. As aresult, many commercially available ceramic brackets have been designedfor the bond to fail at the interface between the bracket and theadhesive to prevent damage to the tooth surface during the debondingprocess. However, this approach results in most of the cured adhesivepad being left behind on the tooth surface after the bracket has beenremoved. Removal of the adhesive pad, which is typically hard andheavily crosslinked, can be time consuming for the clinician anduncomfortable for the patient.

New adhesives and methods are needed that offer satisfactory adhesion ofthe bracket to the tooth surface throughout the treatment process, andalso allow for more convenient removal upon completion of the treatment.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method for reducing thebond strength of an orthodontic appliance adhered to a tooth structurewith a hardened dental composition (e.g., a hardened orthodonticadhesive, a hardened orthodontic cement, and/or a hardened orthodonticprimer) that includes a thermally labile component having one or morethermally labile groups (e.g., cycloaddition adducts and/or oximeesters). In one embodiment, the method includes heating the hardeneddental composition (e.g., to at least 42° C.) to reduce the bondstrength. Preferably, the hardened dental composition maintainssufficient bond strength prior to heating (e.g., throughout the durationof the treatment), but provides reduced bond strength upon heating,allowing for convenient removal of the orthodontic appliance from thetooth structure (e.g., less force required to debond the appliance). Insome embodiments, the thermally labile component and/or dentalcomposition including the same, can be placed so as to result infracture (e.g., adhesive failure) upon debonding at an interface (e.g.,an adhesive-tooth interface or an appliance-adhesive interface), orcohesive failure within the hardened dental composition upon debonding.For example, fracture at an adhesive-tooth interface can result in thehardened adhesive being substantially retained on the removedorthodontic appliance, providing for convenient clean-up of the toothstructure.

In another aspect, the present invention provides a hardenable dentalcomposition (e.g., an orthodontic primer, an orthodontic adhesive, anorthodontic sealant, and/or an orthodontic band cement) that includes ahardenable component having one or more thermally labile groups (e.g.,cycloaddition adducts and/or oxime esters). Articles having suchhardenable dental compositions thereon are also provided, optionally asprecoated articles, and optionally including one or more layers ofdifferent hardenable and/or hardened dental compositions. In someembodiments, the hardenable component having the one or more thermallylabile groups is an ethylenically unsaturated compound. Optionally, thehardenable dental composition further includes additional hardenablecomponents (e.g., ethylenically unsaturated compounds), an initiator forinitiating hardening of the dental composition, a filler, and/or aradiation-to-heat converter. In some embodiments, the hardenable dentalcomposition is a self-etching orthodontic primer or a self-etchingorthodontic adhesive that includes an ethylenically unsaturated compoundwith acid functionality. Methods for making and using such hardenableand/or hardened dental compositions, and articles having such hardenableand/or hardened dental compositions thereon, are also provided.

In yet another aspect, the present invention provides a dentalcomposition including a polymeric thermally labile component. Thepolymeric thermally labile component can include polymeric groups suchas polyurethanes, polyesters, and/or polyamides.

DEFINITIONS

As used herein, “dental composition” refers to a material (e.g., adental or orthodontic material) capable of adhering (e.g., bonding) to atooth structure. Dental compositions include, for example, adhesives(e.g., dental and/or orthodontic adhesives), cements (e.g., glassionomer cements, resin-modified glass ionomer cements, and/ororthodontic cements), primers (e.g., orthodontic primers), restoratives,liners, sealants (e.g., orthodontic sealants), and coatings. Oftentimesa dental composition is used to bond a dental article to a toothstructure.

As used herein, “dental article” refers to an article that can beadhered (e.g., bonded) to a tooth structure. Dental articles include,for example, crowns, bridges. veneers, inlays, onlays, fillings,orthodontic appliances and devices, and prostheses (e.g., partial orfull dentures).

As used herein, “orthodontic appliance” refers to any device intended tobe bonded to a tooth structure, including, but not limited to,orthodontic brackets, buccal tubes, lingual retainers, orthodonticbands, bite openers, buttons, and cleats. The appliance has a base forreceiving adhesive and it can be a flange made of metal, plastic,ceramic, or combinations thereof. Alternatively, the base can be acustom base formed from cured adhesive layer(s) (i.e., single ormulti-layer adhesives).

As used herein, a “packaged” article refers to an orthodontic applianceor card that is received in a container. Preferably, the containerprovides protection from environmental conditions including, forexample, moisture and light.

As used herein, a “release” substrate refers to a substrate in contactwith an article that is removed from the article before or during use ofthe article.

As used herein, a “radiation-to-heat converter” refers to a material orcomposition that absorbs incident radiation (e.g., visible light,ultraviolet (UV) radiation, infrared (IR) radiation, near infrared (NIR)radiation, and/or radio frequency (RF) radiation) and converts asubstantial portion (e.g., at least 50%) of the incident radiation intoheat, which can be useful for softening the thermally responsiveadditive.

As used herein, “softening” refers to loss of modulus of a material thatcan occur as a result of physical and/or chemical changes in thematerial. The degree of softness or deformability of a material issometimes referred to as “compliance” of the material, whereincompliance is defined as the inverse of the Young's modulus of thematerial.

As used herein, “tooth structure” refers to surfaces including, forexample, natural and artificial tooth surfaces, bone, tooth models, andthe like.

As used herein, a “multi-layer” adhesive refers to an adhesive havingtwo or more distinctly different layers (i.e., layers differing incomposition, and preferably having different chemical and/or physicalproperties).

As used herein, a “layer” refers to a discontinuous (e.g., a patternedlayer) or continuous (e.g., non-patterned) material extending across allor a portion of a material different than the layer. The layer may be ofuniform or varying thickness.

As used herein, a “patterned layer” refers to a discontinuous materialextending across (and optionally attached to) only selected portions ofa material different than the patterned layer.

As used herein, a “non-patterned layer” refers to a continuous materialextending across (and optionally attached to) an entire portion of amaterial different than the non-patterned layer.

In general, a layer “on,” “extending across,” or “attached to” anothermaterial different than the layer is intended to be broadly interpretedto optionally include one or more additional layers between the layerand the material different than the layer.

As used herein, “hardenable” is descriptive of a material or compositionthat can be cured (e.g., polymerized or crosslinked) or solidified, forexample, by removing solvent (e.g., by evaporation and/or heating);heating to induce polymerization and/or crosslinking; irradiating toinduce polymerization and/or crosslinking; and/or by mixing one or morecomponents to induce polymerization and/or crosslinking “Mixing” can beperformed, for example, by combining two or more parts and mixing toform a homogeneous composition. Alternatively, two or more parts can beprovided as separate layers that intermix (e.g., spontaneously or uponapplication of shear stress) at the interface to initiatepolymerization.

As used herein, “hardened” refers to a material or composition that hasbeen cured (e.g., polymerized or crosslinked) or solidified.

As used herein, “hardener” refers to something that initiates hardeningof a resin. A hardener may include, for example, a polymerizationinitiator system, a photoinitiator system, and/or a redox initiatorsystem.

As used herein, “photobleachable” refers to loss of color upon exposureto actinic radiation.

As used herein, the term “(meth)acrylate” is a shorthand reference toacrylate, methacrylate, or combinations thereof, and “(meth)acrylic” isa shorthand reference to acrylic, methacrylic, or combinations thereof.

As used herein, the chemical term “group” allows for substitution.

As used herein, “a” or “an” means one or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of an orthodontic appliance having ahardenable or hardened dental composition of the present invention onthe base thereof.

FIG. 2 is a side view of the orthodontic appliance of FIG. 1.

FIG. 3 is a perspective view of a packaged article illustrating anorthodontic appliance having a hardenable or hardened dental compositionof the present invention on the base thereof in a container in which thecover has been partially opened.

FIGS. 4-6 are side views of orthodontic appliances having a plurality oflayers on the bases thereof, in which at least one layer of theplurality of layers is a hardenable or hardened dental composition ofthe present invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The present invention provides hardenable dental compositions, andarticles including such compositions, that are capable of adhering to atooth structure upon hardening. Further, the adherence (e.g., bondstrength) to the tooth structure of such hardened compositions can bereduced upon heating, typically under convenient conditions. The reducedadherence can be useful if and when it is desired to remove the hardenedcomposition from the tooth structure. Such hardenable dentalcompositions encompass materials (e.g., dental and/or orthodonticmaterials) capable of adhering (e.g., bonding) to a tooth structure,such as adhesives (e.g., dental and/or orthodontic adhesives), cements(e.g., glass ionomer cements, resin-modified glass ionomer cements),primers, restoratives, liners, sealants, and coatings. Oftentimes adental composition can be used to bond a dental article (e.g., anorthodontic appliance) to a tooth structure.

In some embodiments, such hardenable dental compositions can, uponhardening, provide sufficient bond strength to adhere an orthodonticappliance to a tooth structure during orthodontic treatment, and arefurther useful for reducing the bond strength, for example, at the endof the treatment process when it is necessary for the practitioner toremove the appliance from the tooth structure. The compositions,articles, and methods are designed to reduce the bond strength uponheating of the hardened dental composition under convenient conditions.The resulting reduced bond strength can allow for convenient removal ofnot only the orthodontic appliance, but also for any hardened dentalcomposition remaining on the tooth structure after removal of theappliance.

Hardenable and hardened dental compositions of the present inventioninclude a thermally labile component, which is described in detailherein. As used herein, a “thermally labile component” refers to acomponent (e.g., a compound) that includes one or more thermally labilegroups. As used herein, a “thermally labile group” refers to a groupthat undergoes substantial breaking of chemical bonds within the groupto form two or more separate groups upon heating to an elevatedtemperature (i.e., at least 42° C.).

A thermally labile component can be incorporated into a wide variety ofdental compositions (e.g., dental and orthodontic materials) including,for example, adhesives, cements (e.g., glass ionomer cements,resin-modified glass ionomer cements), primers, restoratives, liners,sealants, and coatings at levels effective to decrease bond strength ofthe hardened composition upon heating, while maintaining sufficientadhesion (e.g., of an orthodontic appliance) to the tooth structureduring treatment. Treatment can include dental and/or orthodontictreatment processes that last a month, a year, two years, or evenlonger.

For certain embodiments, such dental compositions can be convenientlyapplied to the base of an orthodontic appliance by a practitioner.Alternatively, orthodontic appliances can be provided having such dentalcompositions precoated on the base of the appliance. Typically suchprecoated appliances are provided as packaged articles with or without arelease liner or foam pad liner such as those described, for example, inU.S. Pat. No. 6,183,249 (Brennan et al.). Exemplary containers are wellknown in the art and are disclosed, for example, in U.S. Pat. Nos.5,172,809 (Jacobs et al.) and 6,089,861 (Kelly et al.).

Hardenable dental compositions of the present invention typicallyinclude an ethylenically unsaturated compound, an initiator, and athermally labile component. In some embodiments, the hardenable dentalcomposition also includes a filler. In some embodiments, the hardenabledental composition further includes an ethylenically unsaturatedcompound with acid functionality, wherein the hardenable dentalcomposition can be, for example, a self-etching orthodontic primer or aself-etching orthodontic adhesive. In some embodiments, the hardenabledental composition further includes a radiation-to-heat converter; anacid-generating component and an acid-reactive component; and/or athermally responsive additive, all of which are described hereinafter.Preferably, such compositions, upon hardening, can bond an orthodonticappliance to a tooth structure with a bond strength (using the shearpeel test method described herein) of at least 7 MPa at roomtemperature.

Thermally Labile Components

Hardenable dental compositions of the present invention includethermally labile components. As used herein, a “thermally labilecomponent” refers to a component (typically a compound) that includesone or more thermally labile groups. As used herein, a “thermally labilegroup” refers to a group that undergoes substantial breaking (e.g.,observable by spectroscopic techniques) of chemical bonds within thegroup to form two or more separate groups upon heating to an elevatedtemperature (i.e., at least 42° C.). Preferably, the elevatedtemperature is no greater than 200° C., more preferably no greater than150° C., and even more preferably no greater than 100° C., and mostpreferably no greater than 80° C. Suitable methods for determiningwhether substantial breaking of chemical bonds occurs upon heating acomponent to an elevated temperature would be apparent to one of skillin the art. Suitable methods include, for example, spectroscopic methodssuch as nuclear magnetic resonance (NMR) spectroscopy (including ¹H,¹³C, and/or other appropriate nuclei); and ultraviolet (UV), visible,and infrared (IR) spectroscopy, including near IR (NIR) spectroscopy.For example, ¹H and/or ¹³C NMR spectra can be conveniently run in an NMRtube by dissolving the component in a solvent (e.g., CDCl₃), heating toan elevated temperature, and observing the disappearance of peaksarising from the component or the appearance of peaks arising from areaction product at the desired temperature.

In certain embodiments, a hardened dental composition including athermally labile component softens to a greater extent than the hardeneddental composition not including a thermally labile component, uponheating to a temperature (e.g., no greater than 200° C., preferably nogreater than 150° C., more preferably no greater than 100° C., and mostpreferably no greater than 80° C.). Specifically, upon heating to anelevated temperature (i.e., at least 42° C.), the storage modulus of thehardened dental composition at the elevated temperature decreasescompared to the storage modulus of the hardened dental composition notincluding the thermally labile component at the same elevatedtemperature. Preferably, the storage modulus of the dental compositionat the elevated temperature is at most 60%, more preferably at most 40%,20%, 10%, 5%, 1%, 0.1%, or even 0.01% of the storage modulus of thehardened dental composition not including the thermally labile componentat the same elevated temperature.

Typically and preferably, a hardened dental composition including athermally labile component shows lower bond strength at an elevatedtemperature (e.g., no greater than 200° C., preferably no greater than150° C., more preferably no greater than 100° C., and most preferably nogreater than 80° C.). Specifically, upon heating to an elevatedtemperature (i.e., at least 42° C.), the bond strength of the hardeneddental composition at the elevated temperature decreases compared to thebond strength of the hardened dental composition not including thethermally labile component at the same elevated temperature. Preferably,the bond strength of the dental composition at the elevated temperature(e.g., 70° C.) is at most 90%, more preferably at most 80%, 50%, 30%,20%, or even 10% of the bond strength of the hardened dental compositionnot including the thermally labile component at the same elevatedtemperature (e.g., 70° C.). Further, in certain embodiments it ispreferred that bond strengths at the elevated temperature be maintainedat a sufficient level (e.g., to avoid having brackets fall off into thepatient's mouth before pressure is applied by the practitioner). In suchembodiments, it is preferred that the bond strength of the dentalcomposition at the elevated temperature (e.g., upon exposure to hotfoods) is at least 6 MPa at the elevated temperature.

Preferably, dental compositions including at most 50%, more preferablyat most 30%, 20%, 10%, 5%, or even 1% by weight loading of the thermallylabile component can exhibit such losses in bond strength at an elevatedtemperature. Further, at the same loadings of thermally labilecomponent, preferably the bond strength of the hardened dentalcomposition at room temperature (e.g., 25° C.) is at least 50%, morepreferably at least 70%, 90%, 100%, or even greater than 100% of thebond strength of the hardened dental composition not including thethermally labile component at the same temperature.

In certain embodiments, thermally labile components suitable for use inhardenable dental compositions of the present invention are preferablyhardenable components that include one or more thermally labile groups.Typically, each thermally labile group is a multivalent group linking aplurality (i.e., two or more) of hardenable groups. In certainembodiments, the hardenable thermally labile component is anethylenically unsaturated compound. For example, in such embodiments,the thermally labile group can be a divalent group linking twoethylenically unsaturated groups.

Thermally labile groups are well known in the art. Such groups include,for example, oxime esters as disclosed, for example, in U.S. Pat. No.6,652,970 (Everaerts et al.), and groups including cycloaddition adductsas disclosed, for example, in U.S. Pat. Nos. 6,825,315 (Aubert),6,147,141 (Iyer et al.), and PCT International Patent ApplicationPublication No. WO 98/09913 (Rotello).

In one embodiment, the thermally labile component includes an oximeester. Exemplary thermally labile components including an oxime estercan be represented by the formula (Formula I):

wherein R¹ is hydrogen or an organic group; R² and R³ each independentlyrepresent an organic group that can optionally include, for example, oneor more oxime esters and/or one or more cycloaddition adducts; each E¹and E² independently represents an ethylenically unsaturated group; andm and n are each independently 0 or 1. Two or more groups among R¹, R²,and E¹ can optionally be combined to form one or more rings. R³ and E²can optionally be combined to form one or more rings.

In certain embodiments, R¹ represents hydrogen or a C1 to C10 organicgroup (e.g., a C1 to C10 aliphatic group, and sometimes a C1 to C10aliphatic moiety). Preferably R¹ is hydrogen or methyl. In certainembodiments, R² and R³ each independently represent a C1-C10 organicgroup (e.g., a C1 to C10 aliphatic group, and sometimes a C1 to C10aliphatic moiety).

As used herein, an “ethylenically unsaturated group” refers to a groupthat includes one or more ethylenic unsaturations. Thus, anethylenically unsaturated group can include other substituents inaddition to the one or more ethylenic unsaturations. Each E¹ and E² canindependently represent an ethylenically unsaturated group (i.e., agroup containing a carbon-carbon double bond) selected from a widevariety of ethylenically unsaturated groups including, for example,(meth)acryloyl groups, vinyl groups (including styryl groups such asdivinyl benzene groups), allyl groups, and combinations thereof.

In another embodiment, the thermally labile component includes a groupthat includes a cycloaddition adduct. Exemplary thermally labilecomponents including a cycloaddition adduct can be represented by theformula (Formula II):

wherein R⁴ and R⁵ each independently represent an organic group that canoptionally include, for example, one or more cycloaddition adductsand/or oxime esters; D represents a cycloaddition adduct; each E³ and E⁴independently represents an ethylenically unsaturated group (as definedherein above) or a polymeric group (e.g., a polyester, a polyamide,and/or a polyurethane formed, for example, by the reaction of a hydroxygroup with an isocyanate); and o and p are each independently 0 or 1.Two or more of R⁴, R⁵, E³, E⁴, and/or D can optionally be combined toform one or more rings, with the proviso that the one or more rings donot interfere with the thermal lability of D (i.e., the ability of D toform two or more separate groups upon heating).

In certain embodiments, R⁴ and R⁵ each independently represent a C1 toC10 organic group (e.g., a C1 to C10 aliphatic group, and sometimes a C1to C10 aliphatic moiety).

Cycloaddition adducts can be formed by a variety of cycloadditionreactions that are well known in the art. Suitable cycloadditionreactions include, for example, Diels-Alder reactions, ene reactions,1,3-dipolar additions, [2+2]cycloadditions, and the like. See, forexample, Smith et al., March's Advanced Organic Chemistry: Reactions,Mechanisms, and Structure, Wiley (2001).

In certain embodiments, the cycloaddition adduct is a Diels-Alderadduct, a cyclic adduct that can be formed by a Diels-Alder reactionbetween a diene and a dienophile. See, for example, U.S. Pat. Nos.6,147,141 (Iyer et al.) and 6,825,315 (Aubert), and PCT InternationalPatent Application Publication No. WO 98/09913 (Rotello). Such adductscan be, for example, monocyclic adducts, bicyclic adducts, or tricyclicadducts. For example, when both the diene and the dienophile areacyclic, then a monocyclic adduct is formed. For another example, whenthe diene is monocyclic and the dienophile is acyclic, or when the dieneis acyclic and the dienophile is monocyclic, then a bicyclic adduct isformed. For still another example, when the diene is bicyclic and thedienophile is monocyclic, then a tricyclic adduct is formed.

Suitable diene groups include, for example, butadiene groups,cyclopentadiene groups, furan groups, anthracene groups, andcombinations thereof.

Suitable dienophile groups include, for example, maleic anhydridegroups, maleimide groups, cis and trans cinnamic acid and ester groups,acrylonitrile groups, cyanoethylene groups (including symmetrical andunsymmetrical dicyanoethylene, tricyanoethylene, andtetracyanoethylene), and combinations thereof.

As used herein, the term “organic group” is used for the purpose of thisinvention to mean a hydrocarbon group that is classified as an aliphaticgroup, cyclic group, or combination of aliphatic and cyclic groups(e.g., alkaryl and aralkyl groups). In the context of the presentinvention, suitable groups are those that do not interfere with thehardening of the dental composition or the long-term aging of theadhesive. In the context of the present invention, the term “aliphaticgroup” means a saturated or unsaturated linear or branched hydrocarbongroup. This term is used to encompass alkyl, alkenyl, and alkynylgroups, for example. The term “alkyl group” means a saturated linear orbranched monovalent hydrocarbon group including, for example, methyl,ethyl, n-propyl, isopropyl, tert-butyl, amyl, heptyl, and the like. Theterm “alkenyl group” means an unsaturated, linear or branched monovalenthydrocarbon group with one or more olefinically unsaturated groups(i.e., carbon-carbon double bonds), such as a vinyl group. The term“alkynyl group” means an unsaturated, linear or branched monovalenthydrocarbon group with one or more carbon-carbon triple bonds. The term“cyclic group” means a closed ring hydrocarbon group that is classifiedas an alicyclic group, aromatic group, or heterocyclic group. The term“alicyclic group” means a cyclic hydrocarbon group having propertiesresembling those of aliphatic groups. The term “aromatic group” or “arylgroup” means a mono- or polynuclear aromatic hydrocarbon group. The term“heterocyclic group” means a closed ring hydrocarbon in which one ormore of the atoms in the ring is an element other than carbon (e.g.,nitrogen, oxygen, sulfur, etc.).

As a means of simplifying the discussion and the recitation of certainterminology used throughout this application, the terms “group” and“moiety” (e.g., “organic group” and “organic moiety”) are used todifferentiate between chemical species that allow for substitution orthat may be substituted and those that do not so allow for substitutionor may not be so substituted. Thus, when the term “group” is used todescribe a chemical substituent, the described chemical materialincludes the unsubstituted group and that group with nonperoxidic O, N,S, Si, or F atoms, for example, in the chain as well as carbonyl groupsor other conventional substituents. Where the term “moiety” is used todescribe a chemical compound or substituent, only an unsubstitutedchemical material is intended to be included. For example, the phrase“alkyl group” is intended to include not only pure open chain saturatedhydrocarbon alkyl substituents, such as methyl, ethyl, propyl,tert-butyl, and the like, but also alkyl substituents bearing furthersubstituents known in the art, such as hydroxy, alkoxy, alkylsulfonyl,halogen atoms, cyano, amino, carboxyl, etc. Thus, “alkyl group” includesether groups, haloalkyls, carboxyalkyls, hydroxyalkyls, sulfoalkyls,etc. On the other hand, the phrase “alkyl moiety” is limited to theinclusion of only pure open chain saturated hydrocarbon alkylsubstituents, such as methyl, ethyl, propyl, tert-butyl, and the like.

Thermally labile components can preferably be incorporated into dentalcompositions of the present invention at levels effective to decreasethe bond strength of the hardened dental composition upon heating to thedesired temperature. Preferably, such levels of the thermally labilecomponent also allow for sufficient adhesion during treatment process.Although levels of the thermally labile component will depend on thespecific dental composition being used, typically the hardenable dentalcomposition will include at least 5%, preferably at least 10%, 20%, 30%,or even 50% by weight thermally labile component, based on the totalweight of the dental composition. Typically, the dental composition willinclude at most 95%, preferably at most 90%, 80%, 70%, or even 50% byweight thermally labile component, based on the total weight of thedental composition.

Thermally labile components are typically dissolved, dispersed, orsuspended in, for example, one or more ethylenically unsaturatedcompounds to form the dental composition.

In some embodiments, the thermally labile component is distributeduniformly throughout the hardenable and/or hardened dental composition.In other embodiments, especially for embodiments in which the hardenabledental composition is precoated on the base of an orthodontic appliance,the thermally labile component can be concentrated in a portion of thehardenable dental composition. For example, the thermally labilecomponent can be concentrated near one surface (e.g., the outer surfacethat will contact the tooth structure) to influence the fracture tooccur near the tooth structure upon debonding. A thermally labilecomponent concentrated near one surface is meant to include a thermallylabile component adhered to a surface of the hardenable or hardeneddental composition.

Hardenable Component

The hardenable dental compositions of the present invention typicallyinclude a hardenable (e.g., polymerizable) component, thereby forminghardenable (e.g., polymerizable) compositions. The hardenable componentcan include a wide variety of chemistries, such as ethylenicallyunsaturated compounds (with or without acid functionality), epoxy(oxirane) resins, vinyl ethers, photopolymerization systems, redox curesystems, glass ionomer cements, polyethers, polysiloxanes, and the like.In some embodiments, the compositions can be hardened (e.g., polymerizedby conventional photopolymerization and/or chemical polymerizationtechniques) prior to applying the hardened dental composition. In otherembodiments, a dental composition can be hardened (e.g., polymerized byconventional photopolymerization and/or chemical polymerizationtechniques) after applying the dental composition.

In certain embodiments, the compositions are photopolymerizable, i.e.,the compositions contain a photoinitiator (i.e., a photoinitiatorsystem) that upon irradiation with actinic radiation initiates thepolymerization (or hardening) of the composition. Suchphotopolymerizable compositions can be free radically polymerizable orcationically polymerizable. In other embodiments, the compositions arechemically hardenable, i.e., the compositions contain a chemicalinitiator (i.e., initiator system) that can polymerize, cure, orotherwise harden the composition without dependence on irradiation withactinic radiation. Such chemically hardenable compositions are sometimesreferred to as “self-cure” compositions and may include glass ionomercements (e.g., conventional and resin-modified glass ionomer cements),redox cure systems, and combinations thereof.

Suitable photopolymerizable components that can be used in the dentalcompositions of the present invention include, for example, epoxy resins(which contain cationically active epoxy groups), vinyl ether resins(which contain cationically active vinyl ether groups), ethylenicallyunsaturated compounds (which contain free radically active unsaturatedgroups, e.g., acrylates and methacrylates), and combinations thereof.Also suitable are polymerizable materials that contain both acationically active functional group and a free radically activefunctional group in a single compound. Examples include epoxy-functionalacrylates, epoxy-functional methacrylates, and combinations thereof.

Ethylenically Unsaturated Compounds

The compositions of the present invention may include one or morehardenable components in the form of ethylenically unsaturated compoundswith or without acid functionality, thereby forming hardenablecompositions.

Suitable hardenable compositions may include hardenable components(e.g., photopolymerizable compounds) that include ethylenicallyunsaturated compounds (which contain free radically active unsaturatedgroups). Examples of useful ethylenically unsaturated compounds includeacrylic acid esters, methacrylic acid esters, hydroxy-functional acrylicacid esters, hydroxy-functional methacrylic acid esters, andcombinations thereof.

The compositions (e.g., photopolymerizable compositions) may includecompounds having free radically active functional groups that mayinclude monomers, oligomers, and polymers having one or moreethylenically unsaturated group. Suitable compounds contain at least oneethylenically unsaturated bond and are capable of undergoing additionpolymerization. Such free radically polymerizable compounds includemono-, di- or poly-(meth)acrylates (i.e., acrylates and methacrylates)such as, methyl (meth)acrylate, ethyl acrylate, isopropyl methacrylate,n-hexyl acrylate, stearyl acrylate, allyl acrylate, glyceroltriacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate, 1,3-propanediol di(meth)acrylate,trimethylolpropane triacrylate, 1,2,4-butanetriol trimethacrylate,1,4-cyclohexanediol diacrylate, pentaerythritol tetra(meth)acrylate,sorbitol hexacrylate, tetrahydrofurfuryl (meth)acrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,ethoxylated bisphenolA di(meth)acrylate, andtrishydroxyethyl-isocyanurate trimethacrylate; (meth)acrylamides (i.e.,acrylamides and methacrylamides) such as (meth)acrylamide, methylenebis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane(meth)acrylates; the bis-(meth)acrylates of polyethylene glycols(preferably of molecular weight 200-500), copolymerizable mixtures ofacrylated monomers such as those in U.S. Pat. No. 4,652,274 (Boettcheret al.), acrylated oligomers such as those of U.S. Pat. No. 4,642,126(Zador et al.), and poly(ethylenically unsaturated) carbamoylisocyanurates such as those disclosed in U.S. Pat. No. 4,648,843(Mitra); and vinyl compounds such as styrene, diallyl phthalate, divinylsuccinate, divinyl adipate and divinyl phthalate. Other suitable freeradically polymerizable compounds include siloxane-functional(meth)acrylates as disclosed, for example, in WO-00/38619 (Guggenbergeret al.), WO-01/92271 (Weinmann et al.), WO-01/07444 (Guggenberger etal.), WO-00/42092 (Guggenberger et al.) and fluoropolymer-functional(meth)acrylates as disclosed, for example, in U.S. Pat. No. 5,076,844(Fock et al.), U.S. Pat. No. 4,356,296 (Griffith et al.), EP-0373 384(Wagenknecht et al.), EP-0201 031 (Reiners et al.), and EP-0201 778(Reiners et al.). Mixtures of two or more free radically polymerizablecompounds can be used if desired.

The hardenable component may also contain hydroxyl groups andethylenically unsaturated groups in a single molecule. Examples of suchmaterials include hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl(meth)acrylate and 2-hydroxypropyl (meth)acrylate; glycerol mono- ordi-(meth)acrylate; trimethylolpropane mono- or di-(meth)acrylate;pentaerythritol mono-, di-, and tri-(meth)acrylate; sorbitol mono-, di-,tri-, tetra-, or penta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-ethacryloxypropoxy)phenyl]propane (bisGMA).Suitable ethylenically unsaturated compounds are also available from awide variety of commercial sources, such as Sigma-Aldrich, St. Louis.Mixtures of ethylenically unsaturated compounds can be used if desired.

In certain embodiments hardenable components include PEGDMA(polyethyleneglycol dimethacrylate having a molecular weight ofapproximately 400), bisGMA, UDMA (urethane dimethacrylate), GDMA(glycerol dimethacrylate), TEGDMA (triethyleneglycol dimethacrylate),bisEMA6 as described in U.S. Pat. No. 6,030,606 (Holmes), and NPGDMA(neopentylglycol dimethacrylate). Various combinations of the hardenablecomponents can be used if desired.

Preferably, compositions of the present invention include at least 5% byweight, more preferably at least 10% by weight, and most preferably atleast 15% by weight ethylenically unsaturated compounds, based on thetotal weight of the unfilled composition. Preferably, compositions ofthe present invention include at most 95% by weight, more preferably atmost 90% by weight, and most preferably at most 80% by weightethylenically unsaturated compounds, based on the total weight of theunfilled composition.

Preferably, compositions of the present invention include ethylenicallyunsaturated compounds without acid functionality. Preferably,compositions of the present invention include at least 5% by weight(wt-%), more preferably at least 10% by weight, and most preferably atleast 15% by weight ethylenically unsaturated compounds without acidfunctionality, based on the total weight of the unfilled composition.Preferably, compositions of the present invention include at most 95% byweight, more preferably at most 90% by weight, and most preferably atmost 80% by weight ethylenically unsaturated compounds without acidfunctionality, based on the total weight of the unfilled composition.

Ethylenically Unsaturated Compounds with Acid Functionality

The compositions of the present invention may include one or morehardenable components in the form of ethylenically unsaturated compoundswith acid functionality, thereby forming hardenable compositions.

As used herein, ethylenically unsaturated compounds with acidfunctionality is meant to include monomers, oligomers, and polymershaving ethylenic unsaturation and acid and/or acid-precursorfunctionality. Acid-precursor functionalities include, for example,anhydrides, acid halides, and pyrophosphates. The acid functionality caninclude carboxylic acid functionality, phosphoric acid functionality,phosphonic acid functionality, sulfonic acid functionality, orcombinations thereof.

Ethylenically unsaturated compounds with acid functionality include, forexample, α,β-unsaturated acidic compounds such as glycerol phosphatemono(meth)acrylates, glycerol phosphate di(meth)acrylates, hydroxyethyl(meth)acrylate (e.g., HEMA) phosphates, bis((meth)acryloxyethyl)phosphate, ((meth)acryloxypropyl) phosphate, bis((meth)acryloxypropyl)phosphate, bis((meth)acryloxy)propyloxy phosphate, (meth)acryloxyhexylphosphate, bis((meth)acryloxyhexyl) phosphate, (meth)acryloxyoctylphosphate, bis((meth)acryloxyoctyl) phosphate, (meth)acryloxydecylphosphate, bis((meth)acryloxydecyl) phosphate, caprolactone methacrylatephosphate, citric acid di- or tri-methacrylates, poly(meth)acrylatedoligomaleic acid, poly(meth)acrylated polymaleic acid,poly(meth)acrylated poly(meth)acrylic acid, poly(meth)acrylatedpolycarboxyl-polyphosphonic acid, poly(meth)acrylatedpolychlorophosphoric acid, poly(meth)acrylated polysulfonate,poly(meth)acrylated polyboric acid, and the like, may be used ascomponents in the hardenable component system. Also monomers, oligomers,and polymers of unsaturated carbonic acids such as (meth)acrylic acids,aromatic (meth)acrylated acids (e.g., methacrylated trimellitic acids),and anhydrides thereof can be used. Certain preferred compositions ofthe present invention include an ethylenically unsaturated compound withacid functionality having at least one P—OH moiety.

Certain of these compounds are obtained, for example, as reactionproducts between isocyanatoalkyl (meth)acrylates and carboxylic acids.Additional compounds of this type having both acid-functional andethylenically unsaturated components are described in U.S. Pat. Nos.4,872,936 (Engelbrecht) and 5,130,347 (Mitra). A wide variety of suchcompounds containing both the ethylenically unsaturated and acidmoieties can be used. Mixtures of such compounds can be used if desired.

Additional ethylenically unsaturated compounds with acid functionalityinclude, for example, polymerizable bisphosphonic acids as disclosed forexample, in U.S. Pat. Publication No. 2004/0206932 (Abuelyaman et al.);AA:ITA:IEM (copolymer of acrylic acid:itaconic acid with pendentmethacrylate made by reacting AA:ITA copolymer with sufficient2-isocyanatoethyl methacrylate to convert a portion of the acid groupsof the copolymer to pendent methacrylate groups as described, forexample, in Example 11 of U.S. Pat. No. 5,130,347 (Mitra)); and thoserecited in U.S. Pat. Nos. 4,259,075 (Yamauchi et al.), 4,499,251 (Omuraet al.), 4,537,940 (Omura et al.), 4,539,382 (Omura et al.), 5,530,038(Yamamoto et al.), 6,458,868 (Okada et al.), and European Pat.Application Publication Nos. EP 712,622 (Tokuyama Corp.) and EP1,051,961 (Kuraray Co., Ltd.).

Compositions of the present invention can also include compositions thatinclude combinations of ethylenically unsaturated compounds with acidfunctionality. Preferably the compositions are self-adhesive and arenon-aqueous. For example, such compositions can include: a firstcompound including at least one (meth)acryloxy group and at least one—O—P(O)(OH)_(x) group, wherein x=1 or 2, and wherein the at least one—O—P(O)(OH)_(x) group and the at least one (meth)acryloxy group arelinked together by a C1-C4 hydrocarbon group; a second compoundincluding at least one (meth)acryloxy group and at least one—O—P(O)(OH)_(x) group, wherein x=1 or 2, and wherein the at least one—O—P(O)(OH)_(x) group and the at least one (meth)acryloxy group arelinked together by a C5-C12 hydrocarbon group; an ethylenicallyunsaturated compound without acid functionality; an initiator system;and a filler. Such compositions are described, for example, in U.S.Provisional Application Ser. No. 60/600,658 (Luchterhandt et al.), filedon Aug. 11, 2004.

Preferably, the compositions of the present invention include at least1% by weight, more preferably at least 3% by weight, and most preferablyat least 5% by weight ethylenically unsaturated compounds with acidfunctionality, based on the total weight of the unfilled composition.Preferably, compositions of the present invention include at most 80% byweight, more preferably at most 70% by weight, and most preferably atmost 60% by weight ethylenically unsaturated compounds with acidfunctionality, based on the total weight of the unfilled composition.

Epoxy (Oxirane) or Vinyl Ether Compounds

The hardenable compositions of the present invention may include one ormore hardenable components in the form of epoxy (oxirane) compounds(which contain cationically active epoxy groups) or vinyl ethercompounds (which contain cationically active vinyl ether groups),thereby forming hardenable compositions.

The epoxy or vinyl ether monomers can be used alone as the hardenablecomponent in a dental composition or in combination with other monomerclasses, e.g., ethylenically unsaturated compounds as described herein,and can include as part of their chemical structures aromatic groups,aliphatic groups, cycloaliphatic groups, and combinations thereof.

Examples of epoxy (oxirane) compounds include organic compounds havingan oxirane ring that is polymerizable by ring opening. These materialsinclude monomeric epoxy compounds and epoxides of the polymeric type andcan be aliphatic, cycloaliphatic, aromatic or heterocyclic. Thesecompounds generally have, on the average, at least 1 polymerizable epoxygroup per molecule, in some embodiments at least 1.5, and in otherembodiments at least 2 polymerizable epoxy groups per molecule. Thepolymeric epoxides include linear polymers having terminal epoxy groups(e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers havingskeletal oxirane units (e.g., polybutadiene polyepoxide), and polymershaving pendent epoxy groups (e.g., a glycidyl methacrylate polymer orcopolymer). The epoxides may be pure compounds or may be mixtures ofcompounds containing one, two, or more epoxy groups per molecule. The“average” number of epoxy groups per molecule is determined by dividingthe total number of epoxy groups in the epoxy-containing material by thetotal number of epoxy-containing molecules present.

These epoxy-containing materials may vary from low molecular weightmonomeric materials to high molecular weight polymers and may varygreatly in the nature of their backbone and substituent groups.Illustrative of permissible substituent groups include halogens, estergroups, ethers, sulfonate groups, siloxane groups, carbosilane groups,nitro groups, phosphate groups, and the like. The molecular weight ofthe epoxy-containing materials may vary from 58 to 100,000 or more.

Suitable epoxy-containing materials useful as the resin system reactivecomponents in the present invention are listed in U.S. Pat. Nos.6,187,836 (Oxman et al.) and 6,084,004 (Weinmann et al.).

Other suitable epoxy resins useful as the resin system reactivecomponents include those which contain cyclohexene oxide groups such asepoxycyclohexanecarboxylates, typified by3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexyl-methyl) adipate. For amore detailed list of useful epoxides of this nature, reference is madeto U.S. Pat. Nos. 6,245,828 (Weinmann et al.) and 5,037,861 (Crivello etal.); and U.S. Pat. Publication No. 2003/035899 (Klettke et al.).

Other epoxy resins that may be useful in the compositions of thisinvention include glycidyl ether monomers. Examples are glycidyl ethersof polyhydric phenols obtained by reacting a polyhydric phenol with anexcess of chlorohydrin such as epichlorohydrin (e.g., the diglycidylether of 2,2-bis-(2,3-epoxypropoxyphenol)propane). Further examples ofepoxides of this type are described in U.S. Pat. No. 3,018,262(Schroeder), and in “Handbook of Epoxy Resins” by Lee and Neville,McGraw-Hill Book Co., New York (1967).

Other suitable epoxides useful as the resin system reactive componentsare those that contain silicon, useful examples of which are describedin International Pat. Publication No. WO 01/51540 (Klettke et al.).

Additional suitable epoxides useful as the resin system reactivecomponents include octadecylene oxide, epichlorohydrin, styrene oxide,vinyl cyclohexene oxide, glycidol, glycidylmethacrylate, diglycidylether of Bisphenol A and other commercially available epoxides, asprovided in U.S. Ser. No. 10/719,598 (Oxman et al.; filed Nov. 21,2003).

Blends of various epoxy-containing materials are also contemplated.Examples of such blends include two or more weight average molecularweight distributions of epoxy-containing compounds, such as lowmolecular weight (below 200), intermediate molecular weight (200 to10,000) and higher molecular weight (above 10,000). Alternatively oradditionally, the epoxy resin may contain a blend of epoxy-containingmaterials having different chemical natures, such as aliphatic andaromatic, or functionalities, such as polar and non-polar.

Other types of useful hardenable components having cationically activefunctional groups include vinyl ethers, oxetanes, spiro-orthocarbonates,spiro-orthoesters, and the like.

If desired, both cationically active and free radically activefunctional groups may be contained in a single molecule. Such moleculesmay be obtained, for example, by reacting a di- or poly-epoxide with oneor more equivalents of an ethylenically unsaturated carboxylic acid. Anexample of such a material is the reaction product of UVR-6105(available from Union Carbide) with one equivalent of methacrylic acid.Commercially available materials having epoxy and free-radically activefunctionalities include the CYCLOMER series, such as CYCLOMER M-100,M-101, or A-200 available from Daicel Chemical, Japan, and EBECRYL-3605available from Radcure Specialties, UCB Chemicals, Atlanta, Ga.

The cationically curable components may further include ahydroxyl-containing organic material. Suitable hydroxyl-containingmaterials may be any organic material having hydroxyl functionality ofat least 1, and preferably at least 2. Preferably, thehydroxyl-containing material contains two or more primary or secondaryaliphatic hydroxyl groups (i.e., the hydroxyl group is bonded directlyto a non-aromatic carbon atom). The hydroxyl groups can be terminallysituated, or they can be pendent from a polymer or copolymer. Themolecular weight of the hydroxyl-containing organic material can varyfrom very low (e.g., 32) to very high (e.g., one million or more).Suitable hydroxyl-containing materials can have low molecular weights(i.e., from 32 to 200), intermediate molecular weights (i.e., from 200to 10,000, or high molecular weights (i.e., above 10,000). As usedherein, all molecular weights are weight average molecular weights.

The hydroxyl-containing materials may be non-aromatic in nature or maycontain aromatic functionality. The hydroxyl-containing material mayoptionally contain heteroatoms in the backbone of the molecule, such asnitrogen, oxygen, sulfur, and the like. The hydroxyl-containing materialmay, for example, be selected from naturally occurring or syntheticallyprepared cellulosic materials. The hydroxyl-containing material shouldbe substantially free of groups which may be thermally or photolyticallyunstable; that is, the material should not decompose or liberatevolatile components at temperatures below 100° C. or in the presence ofactinic light which may be encountered during the desiredphotopolymerization conditions for the polymerizable compositions.

Suitable hydroxyl-containing materials useful in the present inventionare listed in U.S. Pat. No. 6,187,836 (Oxman et al.).

The hardenable component(s) may also contain hydroxyl groups andcationically active functional groups in a single molecule. An exampleis a single molecule that includes both hydroxyl groups and epoxygroups.

Glass Ionomers

The hardenable compositions of the present invention may include glassionomer cements such as conventional glass ionomer cements thattypically employ as their main ingredients a homopolymer or copolymer ofan ethylenically unsaturated carboxylic acid (e.g., poly acrylic acid,copoly (acrylic, itaconic acid), and the like), a fluoroaluminosilicate(“FAS”) glass, water, and a chelating agent such as tartaric acid.Conventional glass ionomers (i.e., glass ionomer cements) typically aresupplied in powder/liquid formulations that are mixed just before use.The mixture will undergo self-hardening in the dark due to an ionicreaction between the acidic repeating units of the polycarboxylic acidand cations leached from the glass.

The glass ionomer cements may also include resin-modified glass ionomer(“RMGI”) cements. Like a conventional glass ionomer, an RMGI cementemploys an FAS glass. However, the organic portion of an RMGI isdifferent. In one type of RMGI, the polycarboxylic acid is modified toreplace or end-cap some of the acidic repeating units with pendentcurable groups and a photoinitiator is added to provide a second curemechanism, e.g., as described in U.S. Pat. No. 5,130,347 (Mitra).Acrylate or methacrylate groups are usually employed as the pendantcurable group. In another type of RMGI, the cement includes apolycarboxylic acid, an acrylate or methacrylate-functional monomer anda photoinitiator, e.g., as in Mathis et al., “Properties of a New GlassIonomer/Composite Resin Hybrid Restorative”, Abstract No. 51, J. DentRes., 66:113 (1987) and as in U.S. Pat. Nos. 5,063,257 (Akahane et al.),5,520,725 (Kato et al.), 5,859,089 (Qian), 5,925,715 (Mitra) and5,962,550 (Akahane et al.). In another type of RMGI, the cement mayinclude a polycarboxylic acid, an acrylate or methacrylate-functionalmonomer, and a redox or other chemical cure system, e.g., as describedin U.S. Pat. Nos. 5,154,762 (Mitra et al.), 5,520,725 (Kato et al.), and5,871,360 (Kato). In another type of RMGI, the cement may includevarious monomer-containing or resin-containing components as describedin U.S. Pat. Nos. 4,872,936 (Engelbrecht), 5,227,413 (Mitra), 5,367,002(Huang et al.), and 5,965,632 (Orlowski). RMGI cements are preferablyformulated as powder/liquid or paste/paste systems, and contain water asmixed and applied. The compositions are able to harden in the dark dueto the ionic reaction between the acidic repeating units of thepolycarboxylic acid and cations leached from the glass, and commercialRMGI products typically also cure on exposure of the cement to lightfrom a dental curing lamp. RMGI cements that contain a redox cure systemand that can be cured in the dark without the use of actinic radiationare described in U.S. Pat. No. 6,765,038 (Mitra).

Polyethers or Polysiloxanes (I.E., Silicones)

Dental impression materials are typically based on polyether orpolysiloxane (i.e. silicone) chemistry. Polyether materials typicallyconsist of a two-part system that includes a base component (e.g., apolyether with ethylene imine rings as terminal groups) and a catalyst(or accelerator) component (e.g., an aryl sulfonate as a cross-linkingagent). Polysiloxane materials also typically consist of a two-partsystem that includes a base component (e.g., a polysiloxane, such as adimethylpolysiloxane, of low to moderately low molecular weight) and acatalyst (or accelerator) component (e.g., a low to moderately lowmolecular weight polymer with vinyl terminal groups and chloroplatinicacid catalyst in the case of addition silicones; or a liquid thatconsists of stannous octanoate suspension and an alkyl silicate in thecase of condensation silicones). Both systems also typically contain afiller, a plasticizer, a thickening agent, a coloring agent, or mixturesthereof. Exemplary polyether impression materials include thosedescribed in, for example, U.S. Pat. No. 6,127,449 (Bissinger et al.);U.S. Pat. No. 6,395,801 (Bissinger et al.); and U.S. Pat. No. 5,569,691(Guggenberger et al.). Exemplary polysiloxane impression materials andrelated polysiloxane chemistry are described in, for example, U.S. Pat.Nos. 6,121,362 (Wanek et al.) and 6,566,413 Weinmann et al.), and EPPat. Publication No. 1 475 069 A (Bissinger et al.).

Examples of commercial polyether and polysiloxane impression materialsinclude, but are not limited to, IMPREGUM Polyether Materials, PERMADYNEPolyether Materials, EXPRESS Vinyl Polysiloxane Materials, DIMENSIONVinyl Polysiloxane Materials, and IMPRINT Vinyl Polysiloxane Materials;all available from 3M ESPE (St. Paul, Minn.). Other exemplary polyether,polysiloxane (silicones), and polysulfide impression materials arediscussed in the following reference: Restorative Dental Materials,Tenth Edition, edited by Robert G. Craig and Marcus L. Ward, Mosby-YearBook, Inc., St. Louis, Mo., Chapter 11 (Impression Materials).

Photoinitiator Systems

In certain embodiments, the compositions of the present invention arephotopolymerizable, i.e., the compositions contain a photopolymerizablecomponent and a photoinitiator (i.e., a photoinitiator system) that uponirradiation with actinic radiation initiates the polymerization (orhardening) of the composition. Such photopolymerizable compositions canbe free radically polymerizable or cationically polymerizable.

Suitable photoinitiators (i.e., photoinitiator systems that include oneor more compounds) for polymerizing free radically photopolymerizablecompositions include binary and tertiary systems. Typical tertiaryphotoinitiators include an iodonium salt, a photosensitizer, and anelectron donor compound as described in U.S. Pat. No. 5,545,676(Palazzotto et al.). Preferred iodonium salts are the diaryl iodoniumsalts, e.g., diphenyliodonium chloride, diphenyliodoniumhexafluorophosphate, diphenyliodonium tetrafluoroborate, andtolylcumyliodonium tetrakis(pentafluorophenyl)borate. Preferredphotosensitizers are monoketones and diketones that absorb some lightwithin a range of 400 nm to 520 nm (preferably, 450 nm to 500 nm). Morepreferred compounds are alpha diketones that have some light absorptionwithin a range of 400 nm to 520 nm (even more preferably, 450 to 500nm). Preferred compounds are camphorquinone, benzil, furil,3,3,6,6-tetramethylcyclohexanedione, phenanthraquinone,1-phenyl-1,2-propanedione and other 1-aryl-2-alkyl-1,2-ethanediones, andcyclic alpha diketones. Most preferred is camphorquinone. Preferredelectron donor compounds include substituted amines, e.g., ethyldimethylaminobenzoate. Other suitable tertiary photoinitiator systemsuseful for photopolymerizing cationically polymerizable resins aredescribed, for example, in U.S. Pat. No. 6,765,036 (Dede et al.).

Other suitable photoinitiators for polymerizing free radicallyphotopolymerizable compositions include the class of phosphine oxidesthat typically have a functional wavelength range of 380 nm to 1200 nm.Preferred phosphine oxide free radical initiators with a functionalwavelength range of 380 nm to 450 nm are acyl and bisacyl phosphineoxides such as those described in U.S. Pat. Nos. 4,298,738 (Lechtken etal.), 4,324,744 (Lechtken et al.), 4,385,109 (Lechtken et al.),4,710,523 (Lechtken et al.), and 4,737,593 (Ellrich et al.), 6,251,963(Kohler et al.); and EP Application No. 0 173 567 A2 (Ying).

Commercially available phosphine oxide photoinitiators capable offree-radical initiation when irradiated at wavelength ranges of greaterthan 380 nm to 450 nm include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IRGACURE 819, Ciba Specialty Chemicals, Tarrytown,N.Y.), bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide(CGI 403, Ciba Specialty Chemicals), a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one (IRGACURE 1700, Ciba SpecialtyChemicals), a 1:1 mixture, by weight, ofbis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR 4265, Ciba SpecialtyChemicals), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRINLR8893X, BASF Corp., Charlotte, N.C.).

Typically, the phosphine oxide initiator is present in thephotopolymerizable composition in catalytically effective amounts, suchas from 0.1 weight percent to 5.0 weight percent, based on the totalweight of the composition.

Tertiary amine reducing agents may be used in combination with anacylphosphine oxide. Illustrative tertiary amines useful in theinvention include ethyl 4-(N,N-dimethylamino)benzoate andN,N-dimethylaminoethyl methacrylate. When present, the amine reducingagent is present in the photopolymerizable composition in an amount from0.1 weight percent to 5.0 weight percent, based on the total weight ofthe composition. Useful amounts of other initiators are well known tothose of skill in the art.

Suitable photoinitiators for polymerizing cationicallyphotopolymerizable compositions include binary and tertiary systems.Typical tertiary photoinitiators include an iodonium salt, aphotosensitizer, and an electron donor compound as described in EP 0 897710 (Weinmann et al.); in U.S. Pat. Nos. 5,856,373 (Kaisaki et al.),6,084,004 (Weinmann et al.), 6,187,833 (Oxman et al.), and 6,187,836(Oxman et al.); and in U.S. Pat. No. 6,765,036 (Dede et al.). Thecompositions of the invention can include one or more anthracene-basedcompounds as electron donors. In some embodiments, the compositionscomprise multiple substituted anthracene compounds or a combination of asubstituted anthracene compound with unsubstituted anthracene. Thecombination of these mixed-anthracene electron donors as part of aphotoinitiator system provides significantly enhanced cure depth andcure speed and temperature insensitivity when compared to comparablesingle-donor photoinitiator systems in the same matrix. Suchcompositions with anthracene-based electron donors are described in U.S.Ser. No. 10/719,598 (Oxman et al.; filed Nov. 21, 2003).

Suitable iodonium salts include tolylcumyliodoniumtetrakis(pentafluorophenyl)borate, tolylcumyliodoniumtetrakis(3,5-bis(trifluoromethyl)-phenyl)borate, and the diaryl iodoniumsalts, e.g., diphenyliodonium chloride, diphenyliodoniumhexafluorophosphate, diphenyliodonium hexafluoroantimonate, anddiphenyliodonium tetrafluoroboarate. Suitable photosensitizers aremonoketones and diketones that absorb some light within a range of 450nm to 520 nm (preferably, 450 nm to 500 nm). More suitable compounds arealpha diketones that have some light absorption within a range of 450 nmto 520 nm (even more preferably, 450 nm to 500 nm). Preferred compoundsare camphorquinone, benzil, furil, 3,3,6,6-tetramethylcyclohexanedione,phenanthraquinone and other cyclic alpha diketones. Most preferred iscamphorquinone. Suitable electron donor compounds include substitutedamines, e.g., ethyl 4-(dimethylamino)benzoate and 2-butoxyethyl4-(dimethylamino)benzoate; and polycondensed aromatic compounds (e.g.anthracene).

The initiator system is present in an amount sufficient to provide thedesired rate of hardening (e.g., polymerizing and/or crosslinking). Fora photoinitiator, this amount will be dependent in part on the lightsource, the thickness of the layer to be exposed to radiant energy, andthe extinction coefficient of the photoinitiator. Preferably, theinitiator system is present in a total amount of at least 0.01 wt-%,more preferably, at least 0.03 wt-%, and most preferably, at least 0.05wt-%, based on the weight of the composition. Preferably, the initiatorsystem is present in a total amount of no more than 10 wt-%, morepreferably, no more than 5 wt-%, and most preferably, no more than 2.5wt-%, based on the weight of the composition.

Redox Initiator Systems

In certain embodiments, the compositions of the present invention arechemically hardenable, i.e., the compositions contain a chemicallyhardenable component and a chemical initiator (i.e., initiator system)that can polymerize, cure, or otherwise harden the composition withoutdependence on irradiation with actinic radiation. Such chemicallyhardenable compositions are sometimes referred to as “self-cure”compositions and may include glass ionomer cements, resin-modified glassionomer cements, redox cure systems, and combinations thereof.

The chemically hardenable compositions may include redox cure systemsthat include a hardenable component (e.g., an ethylenically unsaturatedpolymerizable component) and redox agents that include an oxidizingagent and a reducing agent. Suitable hardenable components, redoxagents, optional acid-functional components, and optional fillers thatare useful in the present invention are described in U.S. Pat.Publication Nos. 2003/0166740 (Mitra et al.) and 2003/0195273 (Mitra etal.).

The reducing and oxidizing agents should react with or otherwisecooperate with one another to produce free-radicals capable ofinitiating polymerization of the resin system (e.g., the ethylenicallyunsaturated component). This type of cure is a dark reaction, that is,it is not dependent on the presence of light and can proceed in theabsence of light. The reducing and oxidizing agents are preferablysufficiently shelf-stable and free of undesirable colorization to permittheir storage and use under typical dental conditions. They should besufficiently miscible with the resin system (and preferablywater-soluble) to permit ready dissolution in (and discourage separationfrom) the other components of the hardenable composition.

Useful reducing agents include ascorbic acid, ascorbic acid derivatives,and metal complexed ascorbic acid compounds as described in U.S. Pat.No. 5,501,727 (Wang et al.); amines, especially tertiary amines, such as4-tert-butyl dimethylaniline; aromatic sulfinic salts, such asp-toluenesulfinic salts and benzenesulfinic salts; thioureas, such as1-ethyl-2-thiourea, tetraethyl thiourea, tetramethyl thiourea,1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; and mixtures thereof.Other secondary reducing agents may include cobalt (II) chloride,ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine (dependingon the choice of oxidizing agent), salts of a dithionite or sulfiteanion, and mixtures thereof. Preferably, the reducing agent is an amine.

Suitable oxidizing agents will also be familiar to those skilled in theart, and include but are not limited to persulfuric acid and saltsthereof, such as sodium, potassium, ammonium, cesium, and alkyl ammoniumsalts. Additional oxidizing agents include peroxides such as benzoylperoxides, hydroperoxides such as cumyl hydroperoxide, t-butylhydroperoxide, and amyl hydroperoxide, as well as salts of transitionmetals such as cobalt (III) chloride and ferric chloride, cerium (IV)sulfate, perboric acid and salts thereof, permanganic acid and saltsthereof, perphosphoric acid and salts thereof, and mixtures thereof.

It may be desirable to use more than one oxidizing agent or more thanone reducing agent. Small quantities of transition metal compounds mayalso be added to accelerate the rate of redox cure. In some embodimentsit may be preferred to include a secondary ionic salt to enhance thestability of the polymerizable composition as described in U.S. Pat.Publication No. 2003/0195273 (Mitra et al.).

The reducing and oxidizing agents are present in amounts sufficient topermit an adequate free-radical reaction rate. This can be evaluated bycombining all of the ingredients of the hardenable composition exceptfor the optional filler, and observing whether or not a hardened mass isobtained.

Preferably, the reducing agent is present in an amount of at least 0.01%by weight, and more preferably at least 0.1% by weight, based on thetotal weight (including water) of the components of the hardenablecomposition. Preferably, the reducing agent is present in an amount ofno greater than 10% by weight, and more preferably no greater than 5% byweight, based on the total weight (including water) of the components ofthe hardenable composition.

Preferably, the oxidizing agent is present in an amount of at least0.01% by weight, and more preferably at least 0.10% by weight, based onthe total weight (including water) of the components of the hardenablecomposition. Preferably, the oxidizing agent is present in an amount ofno greater than 10% by weight, and more preferably no greater than 5% byweight, based on the total weight (including water) of the components ofthe hardenable composition.

The reducing or oxidizing agents can be microencapsulated as describedin U.S. Pat. No. 5,154,762 (Mitra et al.). This will generally enhanceshelf stability of the hardenable composition, and if necessary permitpackaging the reducing and oxidizing agents together. For example,through appropriate selection of an encapsulant, the oxidizing andreducing agents can be combined with an acid-functional component andoptional filler and kept in a storage-stable state. Likewise, throughappropriate selection of a water-insoluble encapsulant, the reducing andoxidizing agents can be combined with an FAS glass and water andmaintained in a storage-stable state.

A redox cure system can be combined with other cure systems, e.g., witha hardenable composition such as described U.S. Pat. No. 5,154,762(Mitra et al.).

Fillers

The compositions of the present invention can optionally containfillers. Fillers may be selected from one or more of a wide variety ofmaterials suitable for incorporation in compositions used for dentalapplications, such as fillers currently used in dental restorativecompositions, and the like.

The filler is preferably finely divided. The filler can have a unimodialor polymodial (e.g., bimodal) particle size distribution. Preferably,the maximum particle size (the largest dimension of a particle,typically, the diameter) of the filler is less than 20 micrometers, morepreferably less than 10 micrometers, and most preferably less than 5micrometers. Preferably, the average particle size of the filler is lessthan 0.1 micrometers, and more preferably less than 0.075 micrometer.

The filler can be an inorganic material. It can also be a crosslinkedorganic material that is insoluble in the resin system (i.e., thehardenable components), and is optionally filled with inorganic filler.The filler should in any event be nontoxic and suitable for use in themouth. The filler can be radiopaque or radiolucent. The filler typicallyis substantially insoluble in water.

Examples of suitable inorganic fillers are naturally occurring orsynthetic materials including, but not limited to: quartz (i.e., silica,SiO₂); nitrides (e.g., silicon nitride); glasses and fillers derivedfrom, for example, Zr, Sr, Ce, Sb, Sn, Ba, Zn, and Al; feldspar;borosilicate glass; kaolin; talc; zirconia; titania; low Mohs hardnessfillers such as those described in U.S. Pat. No. 4,695,251 (Randklev);and submicron silica particles (e.g., pyrogenic silicas such as thoseavailable under the trade designations AEROSIL, including “OX 50,”“130,” “150” and “200” silicas from Degussa Corp., Akron, Ohio andCAB-O-SIL M5 silica from Cabot Corp., Tuscola, Ill.). Examples ofsuitable organic filler particles include filled or unfilled pulverizedpolycarbonates, polyepoxides, and the like.

Preferred non-acid-reactive filler particles are quartz (i.e., silica),submicron silica, zirconia, submicron zirconia, and non-vitreousmicroparticles of the type described in U.S. Pat. No. 4,503,169(Randklev). Mixtures of these non-acid-reactive fillers are alsocontemplated, as well as combination fillers made from organic andinorganic materials.

The filler can also be an acid-reactive filler. Suitable acid-reactivefillers include metal oxides, glasses, and metal salts. Typical metaloxides include barium oxide, calcium oxide, magnesium oxide, and zincoxide. Typical glasses include borate glasses, phosphate glasses, andfluoroaluminosilicate (“FAS”) glasses. FAS glasses are particularlypreferred. The FAS glass typically contains sufficient elutable cationsso that a hardened dental composition will form when the glass is mixedwith the components of the hardenable composition. The glass alsotypically contains sufficient elutable fluoride ions so that thehardened composition will have cariostatic properties. The glass can bemade from a melt containing fluoride, alumina, and other glass-formingingredients using techniques familiar to those skilled in the FASglassmaking art. The FAS glass typically is in the form of particlesthat are sufficiently finely divided so that they can conveniently bemixed with the other cement components and will perform well when theresulting mixture is used in the mouth.

Generally, the average particle size (typically, diameter) for the FASglass is no greater than 12 micrometers, typically no greater than 10micrometers, and more typically no greater than 5 micrometers asmeasured using, for example, a sedimentation analyzer. Suitable FASglasses will be familiar to those skilled in the art, and are availablefrom a wide variety of commercial sources, and many are found incurrently available glass ionomer cements such as those commerciallyavailable under the trade designations VITREMER, VITREBOND, RELY XLUTING CEMENT, RELY X LUTING PLUS CEMENT, PHOTAC-FIL QUICK, KETAC-MOLAR,and KETAC-FIL PLUS (3M ESPE Dental Products, St. Paul, Minn.), FUJI IILC and FUJI IX (G-C Dental Industrial Corp., Tokyo, Japan) and CHEMFILSuperior (Dentsply International, York, Pa.). Mixtures of fillers can beused if desired.

The surface of the filler particles can also be treated with a couplingagent in order to enhance the bond between the filler and the resin. Theuse of suitable coupling agents includegamma-methacryloxypropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,and the like. Silane-treated zirconia-silica (ZrO₂—SiO₂) filler,silane-treated silica filler, silane-treated zirconia filler, andcombinations thereof are especially preferred in certain embodiments.

Other suitable fillers are disclosed in U.S. Pat. Nos. 6,387,981 (Zhanget al.) and 6,572,693 (Wu et al.) as well as International PublicationNos. WO 01/30305 (Zhang et al.), WO 01/30306 (Windisch et al.), WO01/30307 (Zhang et al.), and WO 03/063804 (Wu et al.). Filler componentsdescribed in these references include nanosized silica particles,nanosized metal oxide particles, and combinations thereof. Nanofillersare also described in U.S. patent application Ser. Nos. 10/847,781(Kangas et al.); 10/847,782 (Kolb et al.); 10/847,803 (Craig et al.);and 10/847,805 (Budd et al.) all four of which were filed on May 17,2004. These applications, in summary, describe the following nanofillercontaining compositions.

U.S. patent application Ser. No. 10/847,781 (Kangas et al.) describesstable ionomer compositions (e.g., glass ionomer) containing nanofillersthat provide the compositions with improved properties over previousionomer compositions. In one embodiment, the composition is a hardenabledental composition comprising a polyacid (e.g., a polymer having aplurality of acidic repeating groups); an acid-reactive filler; at least10 percent by weight nanofiller or a combination of nanofillers eachhaving an average particle size no more than 200 nanometers; water; andoptionally a polymerizable component (e.g., an ethylenically unsaturatedcompound, optionally with acid functionality).

U.S. patent application Ser. No. 10/847,782 (Kolb et al.) describesstable ionomer (e.g., glass ionomer) compositions containingnanozirconia fillers that provide the compositions with improvedproperties, such as ionomer systems that are optically translucent andradiopaque. The nanozirconia is surface modified with silanes to aid inthe incorporation of the nanozirconia into ionomer compositions, whichgenerally contain a polyacid that might otherwise interact with thenanozirconia causing coagulation or aggregation resulting in undesiredvisual opacity. In one aspect, the composition can be a hardenabledental composition including a polyacid; an acid-reactive filler; ananozirconia filler having a plurality of silane-containing moleculesattached onto the outer surface of the zirconia particles; water; andoptionally a polymerizable component (e.g., an ethylenically unsaturatedcompound, optionally with acid functionality).

U.S. patent application Ser. No. 10/847,803 (Craig et al.) describesstable ionomer compositions (e.g., glass ionomers) containingnanofillers that provide the compositions with enhanced opticaltranslucency. In one embodiment, the composition is a hardenable dentalcomposition including a polyacid (e.g., a polymer having a plurality ofacidic repeating groups); an acid-reactive filler; a nanofiller; anoptional polymerizable component (e.g., an ethylenically unsaturatedcompound, optionally with acid functionality); and water. The refractiveindex of the combined mixture (measured in the hardened state or theunhardened state) of the polyacid, nanofiller, water and optionalpolymerizable component is generally within 4 percent of the refractiveindex of the acid-reactive filler, typically within 3 percent thereof,more typically within 1 percent thereof, and even more typically within0.5 percent thereof.

U.S. patent application Ser. No. 10/847,805 (Budd et al.) describesdental compositions that can include an acid-reactive nanofiller (i.e.,a nanostructured filler) and a hardenable resin (e.g., a polymerizableethylenically unsaturated compound. The acid-reactive nanofiller caninclude an oxyfluoride material that is acid-reactive, non-fused, andincludes a trivalent metal (e.g., alumina), oxygen, fluorine, analkaline earth metal, and optionally silicon and/or a heavy metal.

For some embodiments of the present invention that include filler (e.g.,dental adhesive compositions), the compositions preferably include atleast 1% by weight, more preferably at least 2% by weight, and mostpreferably at least 5% by weight filler, based on the total weight ofthe composition. For such embodiments, compositions of the presentinvention preferably include at most 40% by weight, more preferably atmost 20% by weight, and most preferably at most 15% by weight filler,based on the total weight of the composition.

For other embodiments (e.g., where the composition is a dentalrestorative or an orthodontic adhesive), compositions of the presentinvention preferably include at least 40% by weight, more preferably atleast 45% by weight, and most preferably at least 50% by weight filler,based on the total weight of the composition. For such embodiments,compositions of the present invention preferably include at most 90% byweight, more preferably at most 80% by weight, even more preferably atmost 70% by weight filler, and most preferably at most 50% by weightfiller, based on the total weight of the composition.

Optional Photobleachable and/or Thermochromic Dyes

In some embodiments, compositions of the present invention preferablyhave an initial color remarkably different than dental structures. Coloris preferably imparted to the composition through the use of aphotobleachable or photochromic dye. The composition preferably includesat least 0.001% by weight photobleachable or photochromic dye, and morepreferably at least 0.002% by weight photobleachable or photochromicdye, based on the total weight of the composition. The compositionpreferably includes at most 1% by weight photobleachable or photochromicdye, and more preferably at most 0.1% by weight photobleachable orphotochromic dye, based on the total weight of the composition. Theamount of photobleachable and/or photochromic dye may vary depending onits extinction coefficient, the ability of the human eye to discern theinitial color, and the desired color change. Suitable photobleachabledyes are disclosed, for example, in U.S. Pat. No. 6,670,436 (Burgath etal.).

For embodiments including a photobleachable dye, the color formation andbleaching characteristics of the photobleachable dye varies depending ona variety of factors including, for example, acid strength, dielectricconstant, polarity, amount of oxygen, and moisture content in theatmosphere. However, the bleaching properties of the dye can be readilydetermined by irradiating the composition and evaluating the change incolor. Preferably, at least one photobleachable dye is at leastpartially soluble in a hardenable resin.

Exemplary classes of photobleachable dyes are disclosed, for example, inU.S. Pat. Nos. 6,331,080 (Cole et al.), 6,444,725 (Trom et al.), and6,528,555 (Nikutowski et al.). Preferred dyes include, for example, RoseBengal, Methylene Violet, Methylene Blue, Fluorescein, Eosin Yellow,Eosin Y, Ethyl Eosin, Eosin bluish, Eosin B, Erythrosin B, ErythrosinYellowish Blend, Toluidine Blue, 4′,5′-Dibromofluorescein, andcombinations thereof.

The color change in the inventive compositions is initiated by light.Preferably, the composition's color change is initiated using actinicradiation using, for example, a dental curing light which emits visibleor near infrared (IR) light for a sufficient amount of time. Themechanism that initiates the color change in the compositions of theinvention may be separate from or substantially simultaneous with thehardening mechanism that hardens the resin. For example, a compositionmay harden when polymerization is initiated chemically (e.g., redoxinitiation) or thermally, and the color change from an initial color toa final color may occur subsequent to the hardening process uponexposure to actinic radiation.

The change in composition color from an initial color to a final coloris preferably quantified by a color test. Using a color test, a value ofΔE* is determined, which indicates the total color change in a3-dimensional color space. The human eye can detect a color change ofapproximately 3 ΔE* units in normal lighting conditions. The dentalcompositions of the present invention are preferably capable of having acolor change, ΔE*, of at least 20; more preferably, ΔE* is at least 30;most preferably ΔE* is at least 40.

Optional Acid-Generating Component and Acid-Reactive Component

Optionally, the hardenable dental composition of the present inventioncan include an acid-generating component and an acid-reactive componentas described, for example, in U.S. Pat. Application Publication No.2007/0142497 A1 (Kalgutkar et al.).

Acid-generating components typically include an acid-generatingcompound, and optionally a sensitizer. Preferably, the acid-generatingcomponent generates an acid upon irradiation (i.e., a photo-acid).Typically, the acid can react with greater than a stoichiometric amountof acid-reactive groups. Preferably, dental compositions of the presentinvention do not include groups that would act to deplete the generatedacid in amounts sufficient to interfere with the desired reaction of thegenerated acid with the acid-reactive component.

Exemplary acid-generating components include iodonium salts (e.g.,diaryliodonium salts), sulfonium salts (e.g., triarylsulfonium salts anddialkylphenacylsulfonium salts), selenonium salts (e.g.,triarylselenonium salts), sulfoxonium salts (e.g., triarylsulfoxoniumsalts, aryloxydiarylsulfoxonium salts, and dialkylphenacylsulfoxoniumsalts), diazonium salts (e.g., aryldiazonium salts), organometalliccomplex cations (e.g., ferrocenium salts), halo-S-triazenes,trihaloketones, α-sulfonyloxy ketones, silyl benzyl ethers, andcombinations thereof. When the acid-generating component is a salt of acationic species (e.g., an “onium” salt), typical counterions for thesalt include, for example, tetrafluoroborate, hexafluorophosphate,hexafluoroarsenate, hexafluoroantimonate, and combinations thereof.Exemplary acid-generating components include those disclosed, forexample, in Crivello et al., “Photoinitiators for Free Radical, Cationicand Anionic Photopolymerization,” G. Bradley, Editor, Volume 3, Chapter6 (1998), and U.S. Pat. Nos. 6,187,833 (Oxman et al.), 6,395,124 (Oxmanet al.), 6,765,036 (Dede et al.), 3,775,113 (Bonham et al.), 3,779,778(Smith et al.), 3,954,475 (Bonham et al.), 4,329,384 (Vesley et al.),4,330,570 (Giuliani et al.), 5,089,374 (Saeva), and 5,141,969 (Saeve etal.).

Preferably the acid-generating component includes a sulfonium salt.Exemplary sulfonium salts include, for example, triaryl sulfoniumhexafluoroantimonate (Ar₃S⁺SbF₆ ⁻, available under the trade designationCYRACURE CPI-6976 from Advanced Research Corporation, Catoosa, Okla.);triaryl sulfonium hexafluorophosphate (Ar₃S⁺PF₆ ⁻, 50% solution inpropylene carbonate, available under the trade designation CYRACURECPI-6992, from Aceto Corp., Lake Success, N.Y.); and triaryl sulfoniumN-(trifluoromethanesulfonyl)trifluoromethane-sulfonamido anion(Ar₃S⁺N(SO₂CF₃)₂)⁻, which can be prepared as generally described in U.S.Pat. No. 5,554,664 (Lamanna et al.).

Exemplary sensitizers include anthracene derivatives (e.g.,2-methylanthracene (2-MA, Sigma-Aldrich) and2-ethyl-9,10-dimethoxyanthracene (EDMOA, Sigma-Aldrich)), perylene,phenothiazene, and other polycyclic aromatic compounds as described, forexample, in U.S. Pat. No. 6,765,036 (Dede et al.) and U.S. Pat.Publication No. 2005/0113477 (Oxman et al.), and combinations thereof.One of skill in the art could select, without undue experimentation, anappropriate sensitizer for sensitizing a specific acid-generatingcomponent (e.g., a sulfonium salt) based on the principles described,for example, in Crivello et al., “Photoinitiators for Free Radical,Cationic and Anionic Photopolymerization,” G. Bradley, Editor, Volume 3,Chapter 6 (1998). Preferably, a sensitizer can be selected that absorbsat a different wavelength than the photoinitiator; has a singlet ortriplet state that is higher in energy than the corresponding singlet ortriplet state in the acid-generating component; and/or has an oxidationpotential such that reduction of the acid-generating component isenergetically favorable. For example, 2-methylanthracene is anappropriate sensitizer for sensitizing triaryl sulfoniumhexafluoroantimonate.

As used herein, an “acid-reactive component” refers to a component(typically a compound) that includes one or more acid-reactive groups.As used herein, an “acid-reactive group” refers to a group thatundergoes, after reaction with an acid, substantial breaking (e.g.,observable by spectroscopic techniques) of chemical bonds within thegroup to form two or more separate groups, often upon heating to anelevated temperature (i.e., at least 42° C.). Preferably, the elevatedtemperature is no greater than 200° C., more preferably no greater than150° C., and even more preferably no greater than 100° C., and mostpreferably no greater than 80° C. Suitable methods for determiningwhether substantial breaking of chemical bonds occurs after reaction ofa component with an acid would be apparent to one of skill in the art.Suitable methods include, for example, spectroscopic methods such asnuclear magnetic resonance (NMR) spectroscopy (including ¹H, ¹³C, and/orother appropriate nuclei); and ultraviolet (UV), visible, and infrared(IR) spectroscopy, including near IR (NIR) spectroscopy. For example, ¹Hand/or ¹³C NMR spectra can be conveniently run in an NMR tube bydissolving the component in a non-acidic solvent (e.g., CDCl₃), addingan acid (e.g., CF₃CO₂D), and observing the disappearance of peaksarising from the component or the appearance of peaks arising from areaction product at the desired temperature.

Acid-reactive components suitable for use in hardenable dentalcompositions of the present invention are preferably hardenablecomponents that include one or more acid-reactive groups. Typically,each acid-reactive group is a multivalent group linking a plurality(i.e., two or more) of hardenable groups. In certain embodiments, thehardenable acid-reactive component is an ethylenically unsaturatedcompound. For example, in such embodiments, the acid-reactive group canbe a divalent group linking two ethylenically unsaturated groups.

Acid reactive groups are well known in the art. Such groups include, forexample, functionalities typically used in protection methodologies inorganic synthesis, where the protecting group can be designed forremoval under acidic conditions. See, for example, Greene et al.Protective Groups in Organic Synthesis, Wiley-Interscience (1999);Taylor et al., Chem. Mater., 3:1031-1040 (1991); and U.S. Pat. No.6,652,970 (Everaerts et al.).

Optional Thermally Responsive Additives

Optionally, the hardenable dental composition of the present inventioncan include a thermally responsive additive as described, for example,in U.S. Pat. Application Publication No. 2007/0142498 A1 (Brennan etal.).

As used herein, a “thermally responsive additive” is meant to include anadditive that softens upon heating to a temperature (e.g., no greaterthan 200° C., preferably no greater than 150° C., more preferably nogreater than 100° C., and most preferably no greater than 80° C.) thatis below the decomposition temperature of the additive. Specifically,upon heating to an elevated temperature (i.e., at least 42° C.), thestorage modulus of the additive at the elevated temperature decreasescompared to the storage modulus of the additive at room temperature(e.g., 25° C.). Preferably, the storage modulus of the additive at theelevated temperature is at most 80%, more preferably at most 60%, 40%,20%, 10%, 5%, 2%, 1%, 0.1%, or even 0.01% of the storage modulus of theadditive at room temperature. Methods of measuring storage modulus ofmaterials at specified temperatures are well known in the art andinclude those described, for example, in Rudin, “The Elements of PolymerScience and Engineering,” 2^(nd) Ed, Chapter 11, pp. (1999). Suchmethods include, for example, dynamic mechanical measurements bytechniques such as dynamic mechanical analysis (DMA).

Such thermally responsive additives typically have a maximum in the rateof storage modulus decrease occurring typically within the range of 42°C. to 200° C. Such a maximum in the rate of storage modulus decrease cancorrespond to transitions including, for example, melt transitions(T_(m)), glass transitions (T_(g)), solid to smectic or nematic phasetransitions in liquid crystals, isotropic melt transitions in liquidcrystals, and the like.

In certain embodiments, softening of a hardened dental compositionincluding a thermally responsive additive, upon heating to a temperature(e.g., no greater than 200° C., preferably no greater than 150° C., morepreferably no greater than 100° C., and most preferably no greater than80° C.) that is below the decomposition temperature of the additive, mayoptionally, but not necessarily, be observed to a greater extent thanfor the hardened dental composition not including a thermally responsiveadditive under similar conditions.

In some embodiments, thermally responsive additives can be polymers.Polymers having a wide variety of morphologies can be used. For example,a thermally responsive additive can be a semicrystalline polymer, anamorphous polymer, or a combination thereof. In some embodiments,thermally responsive additives can be liquid crystals (e.g.,non-polymeric liquid crystals or polymeric liquid crystals). In someembodiments, thermally responsive additives can be waxes.

Useful semicrystalline polymers typically have a melt transitiontemperature (T_(m)) of at least 42° C. Useful semicrystalline polymerstypically have a melt transition temperature (T_(m)) of at most 200° C.,preferably at most 150° C., more preferably at most 100° C., and mostpreferably no greater than 80° C.

Useful amorphous polymers typically have a glass transition temperature(T_(g)) of at least 42° C. Useful amorphous polymers typically have aglass transition temperature (T_(g)) of at most 200° C., preferably atmost 150° C., more preferably at most 100° C., and most preferably nogreater than 80° C.

Examples of polymer classes that can be used for thermally responsiveadditives include poly((meth)acrylics), poly((meth)acrylamides),poly(alkenes), poly(dienes), poly(styrenes), poly(vinyl alcohol),poly(vinyl ketones), poly(vinyl esters), poly(vinyl ethers), poly(vinylthioethers), poly(vinyl halides), poly(vinyl nitriles),poly(phenylenes), poly(anhydrides), poly(carbonates), poly(esters),poly(lactones), poly(ether ketones), poly(alkylene oxides),poly(urethanes), poly(siloxanes), poly(sulfides), poly(sulfones),poly(sulfonamides), poly(thioesters), poly(amides), poly(anilines),poly(imides), poly(imines), poly(ureas), poly(phosphazenes),poly(silanes), poly(silazanes), carbohydrates, gelatins, poly(acetals),poly(benzoxazoles), poly(carboranes), poly(oxadiazoles),poly(piperazines), poly(piperidines), poly(pyrazoles), poly(pyridines),poly(pyrrolidines), poly(triazines), and combinations thereof. One ofskill in the art could select, without undue experimentation, polymersfrom the above-recited classes that have desired transitiontemperatures. See, for example, “Polymer Handbook,” 4^(th) Editionedited by J. Brandrup et al. (1999) for a list of melt transitiontemperatures and glass transition temperatures of selected polymers.

A wide variety of liquid crystals can be used for thermally responsiveadditives including, for example, those recited in “Liquid CrystalsHandbook,” volumes 1-3, edited by Demus et al. (1998). Suitable liquidcrystals typically have an isotropic transition temperature of at least42° C. Suitable liquid crystals typically have an isotropic transitiontemperature of at most 200° C., preferably at most 150° C., morepreferably at most 100° C., and most preferably no greater than 80° C.One of skill in the art could select, without undue experimentation,liquid crystals that have desired transition temperatures.

Useful classes of liquid crystals include, for example, biphenyls (e.g.,R-Ph-Ph-CN); terphenyls (e.g., R-Ph-Ph-Ph-CN); esters (e.g.,R-PhC(O)O-Ph-OR′, R-PhC(O)O-Ph-CN, and R-PhC(O)O-Ph-Ph-CN); tolanes(e.g., R-Ph-CC-Ph-OR′); Schiffs bases (e.g., R-Ph-N═CH-Ph-OR′ andR—O-Ph-CH═N-Ph-CN); azo compounds (R-Ph-N═N-Ph-OR′); azoxy compounds(e.g., R-Ph-N═N⁺(O⁻)-Ph-OR′); and stilbenes (e.g.,R-Ph-C(Cl)═CH-Ph-OR′), where each R and R′ independently represent analkyl group. R is preferably a higher alkyl group, and typically atleast a C7 alkyl group, and sometimes at least a C12 alkyl group. R′ ispreferably a lower alkyl group, and typically a C1 or C2 alkyl group.

Examples of waxes that can be used for thermally responsive additivesinclude dental waxes such as pattern wax, base-plate wax, sheet wax,impression wax, study wax, polycaprolactone, polyvinylacetate,ethylene-vinyl acetate copolymer, polyethylene glycol, esters ofcarboxylic acids with long chain alcohols (e.g., behenyl acrylate),esters of long chain carboxylic acids with long chain alcohols (e.g.,beeswax, a non-polymeric wax), petroleum waxes, oxidized polyethylenewax (e.g., a wax available under the trade designation CERIDUST 3719from Clariant Corp., Charlotte, N.C.), micronized, polar, high densitypolyethylene wax (e.g., a wax available under the trade designationCERIDUST 3731 from Clariant Corp., Charlotte, N.C.), carnauba wax (e.g.,a wax available under the trade designation MIWAX from MichelmanIncorporated, Cincinnati, Ohio), and combinations thereof (e.g., blendsincluding two or more of microcystalline waxes, carnauba wax, ceresin,and beeswax). Useful waxes can also be oligomeric or polymeric. Usefulwaxes can be macrocrystalline or microcrystalline, natural or synthetic,and they may contain functional groups (e.g., carboxyl, alcohol, ester,ketone, and/or amide groups). Suitable waxes melt at or above roomtemperature (e.g., 25° C.), and typically at or above 40° C., andsometimes at or above 50° C. Suitable waxes typically have low melttemperatures (e.g., no greater than 200° C., preferably no greater than150° C., more preferably no greater than 100° C., even more preferablyno greater than 90° C., and most preferably no greater than 80° C.).Suitable waxes can have a wide variety of physical properties. Forexample, at room temperature, physical properties of suitable waxes canrange from kneadable to hard or brittle; coarse to crystalline; and/ortransparent to opaque (with transparent being preferred).

Optional Radiation-to-Heat Converters

Optionally, the hardenable dental composition of the present inventioncan include a radiation-to-heat converter as described, for example, inU.S. Pat. Application Publication No. 2007/0141524 A1 (Brennan et al.).Hardened dental compositions that include a radiation-to-heat convertercan allow for heating the hardened dental composition by irradiating thecomposition.

A radiation-to-heat converter is typically a radiation absorber thatabsorbs incident radiation and converts at least a portion (e.g., atleast 50%) of the incident radiation into heat. In some embodiments, theradiation-to-heat converter can absorb light in the infrared, visible,or ultraviolet regions of the electromagnetic spectrum and convert theabsorbed radiation into heat. In other embodiments, theradiation-to-heat converter can absorb radio frequency (RF) radiationand convert the absorbed radiation into heat. The radiation absorber(s)are typically highly absorptive of the selected imaging radiation.

A wide variety of radiation-to-heat converters can be used including,for example, organic compounds, inorganic compounds, and metal-organiccompounds. Such radiation-to-heat converters can include, for example,dyes (e.g., visible dyes, ultraviolet dyes, infrared dyes, fluorescentdyes, and radiation-polarizing dyes), pigments, metals, metal compounds,metal films, and other suitable absorbing materials. Many classes oforganic and metal-organic dyes are described in “Infrared AbsorbingDyes”, edited by Masaru Matsuoka, Plenum Press (New York, 1990). Theseclasses of dyes include azo dyes, pyrazolone azo dyes, methine andcyanine dyes, porphyrin dyes, phthalocyanine dyes, quinine dyes such asanthraquinones and naphthaquinones, pyrylium and squarylium dyes,aminium and diimonium dyes. See, also, U.S. Pat. No. 6,759,177 (Shimadaet al.). Radiation-to-heat converters can be selected as desired by oneof skill in the art based on properties including, for example,solubility in and/or compatibility with the specific hardenable dentalcomposition or solvent therefore, as well as the wavelength range ofabsorption. Typically, dyes and/or pigments are preferred for use asradiation-to-heat converters that absorb light in the infrared, visible,or ultraviolet regions of the electromagnetic spectrum.

For some embodiments, near infrared (NIR) absorbing pigments and/or dyesare preferred by use as radiation-to-heat converters to allow forheating by irradiating with NIR radiation. Such NIR absorbing materialstypically absorb at wavelengths greater than 750 nanometers, andsometimes at wavelengths greater than 800, 850, or even 900 nanometers.Such NIR absorbing materials typically absorb at wavelengths less than2000 nanometers, and sometimes at wavelengths less than 1500, 1200, oreven 1000 nanometers.

A wide variety of pigments and/or dyes can be used as NIR absorbingradiation-to-heat converters. Useful pigments include, for example,indium tin oxide (ITO), antimony tin oxide (ATO), other tin oxidepigments, lanthanum hexaboride (LAB₆), porphyrin and phthalocyaninepigments, thioindigo pigments, carbon black, azo pigments, quinacridonepigments, nitroso pigments, natural pigments, and azine pigments. Usefuldyes include, for example, NIR absorbing cyanine dyes, NIR absorbing azodyes, NIR absorbing pyrazolone dyes, NIR absorbing phthalocyanine dyes,NIR absorbing anthraquinone and naphthaquinone dyes, nickel or platinumdithiolene complexes, squarilium dyes, carbonium dyes, methine dyes,diimonium dyes, aminium dyes, croconium dyes, quinoneimine dyes, andpyrylium dyes such as those available under the trade designations IR-27and IR-140 from Sigma-Aldrich (St. Louis, Mo.) or Epolin Inc. (Newark,N.J.).

In some embodiments, the radiation-to-heat converter can be a radiofrequency (RF) absorbing magnetic ceramic powder, to allow for heatingby irradiating with RF radiation. Exemplary ceramic powders include, forexample, NiZn ferrite available under the trade designation FERRITE N23from National Magnetics Group (Bethlehem, Pa.) with a reported averageparticle size of 1.0 micrometer and a Curie Temperature (T_(c)) of 95°C.; and Mg—Mn—Zn mixed ferrite available under the trade designationFERRITE R from National Magnetics Group (Bethlehem, Pa.) with a reportedaverage particle size of 1.0 micrometer and a Curie Temperature (T_(c))of 90° C. Such ceramic powders are capable of absorbing radio frequency(RF) radiation and thereby increasing in temperature. At the reportedCurie Temperatures, the ferrites will no longer absorb RF radiation andcontinue to increase in temperature. Typical RF radiation useful in thisinvention has an intensity range of 10 μW/cm² to 100 μW/cm² and afrequency of 10 KHz to 10 KHz.

Miscellaneous Optional Additives

Optionally, compositions of the present invention may contain solvents(e.g., alcohols (e.g., propanol, ethanol), ketones (e.g., acetone,methyl ethyl ketone), esters (e.g., ethyl acetate), other nonaqueoussolvents (e.g., dimethylformamide, dimethylacetamide, dimethylsulfoxide,1-methyl-2-pyrrolidinone)), and water.

If desired, the compositions of the invention can contain additives suchas indicators, dyes, pigments, inhibitors, accelerators, viscositymodifiers, wetting agents, buffering agents, stabilizers, and othersimilar ingredients that will be apparent to those skilled in the art.Viscosity modifiers include the thermally responsive viscosity modifiers(such as PLURONIC F-127 and F-108 available from BASF WyandotteCorporation, Parsippany, N.J.) and may optionally include apolymerizable moiety on the modifier or a polymerizable componentdifferent than the modifier. Such thermally responsive viscositymodifiers are described in U.S. Pat. No. 6,669,927 (Trom et al.) andU.S. Pat. Publication No. 2004/0151691 (Oxman et al.).

Additionally, medicaments or other therapeutic substances can beoptionally added to the dental compositions. Examples include, but arenot limited to, fluoride sources, whitening agents, anticaries agents(e.g., xylitol), calcium sources, phosphorus sources, remineralizingagents (e.g., calcium phosphate compounds), enzymes, breath fresheners,anesthetics, clotting agents, acid neutralizers, chemotherapeuticagents, immune response modifiers, thixotropes, polyols,anti-inflammatory agents, antimicrobial agents (in addition to theantimicrobial lipid component), antifungal agents, agents for treatingxerostomia, desensitizers, and the like, of the type often used indental compositions. Combination of any of the above additives may alsobe employed. The selection and amount of any one such additive can beselected by one of skill in the art to accomplish the desired resultwithout undue experimentation.

Methods

Hardenable and hardened dental compositions of the present invention(e.g., compositions that in certain embodiments include a thermallylabile component including one or more thermally labile groups) can beused for a variety of dental and orthodontic applications that utilize amaterial capable of adhering (e.g., bonding) to a tooth structure.Preferred uses include applications in which it is desired that thehardened dental composition be removed from the tooth structure at somepoint in time. Uses for such hardenable and hardened dental compositionsinclude, for example, uses as adhesives (e.g., dental and/or orthodonticadhesives), cements (e.g., glass ionomer cements, resin-modified glassionomer cements, and orthodontic cements), primers (e.g., orthodonticprimers), restoratives, liners, sealants (e.g., orthodontic sealants),coatings, and combinations thereof.

One preferred use for such hardenable or hardened dental compositionsincludes adhering an orthodontic appliance to a tooth structure.Exemplary embodiments for an orthodontic appliance having a hardenableor hardened dental composition of the present invention on the basethereof are illustrated in FIGS. 1-6. It should be noted that for suchembodiments, a practitioner can apply the hardenable dental compositionto the base of the orthodontic appliance, and then optionally harden thecomposition. Alternatively, an orthodontic appliance having a hardenable(or hardened) dental composition on the base thereof can be supplied,for example, by a manufacturer, as a “precoated” orthodontic appliance.In yet other embodiments, a practitioner can apply a hardenable dentalcomposition (e.g., an orthodontic primer) to a tooth structure,optionally harden the composition, and then adhere the orthodonticappliance (typically having a hardenable orthodontic adhesive thereon)to the tooth structure.

In FIGS. 1 and 2, an exemplary orthodontic appliance is designated bythe numeral 10 and is a bracket, although other appliances such asbuccal tubes, buttons and other attachments are also possible. Theappliance 10 includes a base 12. The appliance 10 also has a body 14that extends outwardly from the base 12. Base 12 can be a flange made ofmetal, plastic, ceramic, and combinations thereof. Base 12 can include amesh-like structure, such as a fine wire screen. Base 12 can includeparticles (such as shards, grit, spheres, or other structure thatoptionally includes undercuts). Alternatively, the base 12 can be acustom base formed from one or more hardened dental composition layer(s)(e.g., hardened dental compositions of the present invention, hardenedorthodontic adhesives, hardened orthodontic primers, or combinationsthereof). Tiewings 16 are connected to the body 14, and an archwire slot18 extends through a space between the tiewings 16. The base 12, thebody 14, and tiewings 16 may be made of any one of a number of materialssuitable for use in the oral cavity and having sufficient strength towithstand the correction forces applied during treatment. Suitablematerials include, for example, metallic materials (such as stainlesssteel), ceramic materials (such as monocrystalline or polycrystallinealumina), and plastic materials (such as fiber-reinforcedpolycarbonate). Optionally, the base 12, the body 14, and the tiewings16 are integrally made as a unitary component.

In the exemplary embodiment illustrated in FIGS. 1 and 2, a layer of ahardenable or hardened dental composition of the present invention 22(hereinafter “composition layer 22”), which is typically an orthodonticadhesive, an orthodontic primer, or an orthodontic sealant, extendsacross the base 12 of the appliance 10. The composition layer 22 canserve in whole or at least in part to securely fix the appliance 10 tothe patient's tooth by a bond having sufficient strength to resistunintended detachment from the tooth during the course of treatment. Inone embodiment, the composition layer 22 is applied by the manufacturerto the base 12 of the appliance 10. It should be understood thatorthodontic appliance 10 can optionally include additional layer(s) ofdental compositions (e.g., orthodontic adhesives, orthodontic primers,or combinations thereof, which are not illustrated in FIGS. 1 and 2) incontact with composition layer 22. Specifically, such additionallayer(s) can be between base 12 and composition layer 22; on compositionlayer 22 opposite base 12; or both. Such layers may or may not cover thesame area, and may independently be discontinuous (e.g., a patternedlayer) or continuous (e.g., non-patterned) materials extending acrossall or a portion of adhesive 22. Exemplary appliances including suchadditional layer(s) are illustrated in FIGS. 4-6.

Orthodontic appliances including multiple hardenable or hardened dentalcomposition layers as described herein can be prepared by methods knownto one of skill in the art. Suitable methods include, for example,applying, dispensing, or printing the layers of composition on anappliance or a substrate. Multiple layers may be applied simultaneouslyor sequentially.

A useful method for applying multiple layers of hardenable dentalcomposition(s) on an orthodontic appliance or a substrate includes, forexample, using automated fluid dispensing systems such as thoseavailable under the trade designation AUTOMOVE from Asymtek (Carlsbad,Calif.). Such automated fluid dispensing systems are useful fordispensing both patterned and non-patterned layers. Other useful systemsinclude, for example, piston dispensing systems and multiple resolutionfluid applicators as described, for example, in U.S. Pat. No. 6,513,897(Tokie) and U.S. Pat. Application Publication No. 2005/0136370 A1(Brennan et al.).

Once the hardenable dental composition layer(s) have been applied to anorthodontic appliance or a substrate, the appliance or substrate canconveniently be packaged in a container. Exemplary containers are wellknown in the art and are disclosed, for example, in U.S. Pat. Nos.5,172,809 (Jacobs et al.) and 6,089,861 (Kelly et al.).

Referring to FIG. 3, an exemplary embodiment of packaged article 40including orthodontic appliance 42 having hardenable dental compositionlayer(s) coated on the base thereof is shown. Package 44 includescontainer 46 and cover 48. Cover 48, which is releasably connected tocontainer 46 as initially provided, is peeled from container 46 to openthe package for removal of orthodontic appliance 42. In FIG. 3, cover 48has been peeled back from container 46 to partially open package 44.

In preferred embodiments, the package provides excellent protectionagainst degradation of the hardenable dental composition(s) (e.g.,photocurable materials), even after extended periods of time. Suchcontainers are particularly useful for protecting dyes that impart acolor changing feature to the adhesive. Such containers preferablyeffectively block the passage of actinic radiation over a broad spectralrange, and as a result, the compositions do not prematurely lose colorduring storage.

In preferred embodiments, the package includes container 46 comprising apolymer and metallic particles. As an example, container 46 may be madeof polypropylene that is compounded with aluminum filler or receives analuminum powder coating as disclosed, for example, in U.S. Pat.Application Publication No. 2003/0196914 A1 (Tzou et al.). Thecombination of polymer and metallic particles provides a highlyeffective block to the passage of actinic radiation to color changingdyes, even though such dyes are known to be highly sensitive to light.Such containers also exhibit good vapor barrier properties. As a result,the rheological characteristics of the hardenable dental composition(s)are less likely to change over extended periods of time. For example,the improved vapor barrier properties of such containers providesubstantial protection against degradation of the handlingcharacteristics of adhesives so that the compositions do not prematurelycure or dry or become otherwise unsatisfactory. Suitable covers 48 forsuch containers can be made of any material that is substantially opaqueto the transmission of actinic radiation so that the compositions do notprematurely cure. Examples of suitable materials for cover 48 includelaminates of aluminum foil and polymers. For example, the laminate maycomprise a layer of polyethyleneterephthalate, adhesive, aluminum foil,adhesive and oriented polypropylene.

In some embodiments, a packaged orthodontic appliance including ahardenable dental composition of the present invention thereon mayinclude a release substrate as described, for example, in U.S. Pat. No.6,183,249 (Brennan et al.).

In other embodiments, a packaged orthodontic appliance including ahardenable dental composition of the present invention thereon may notinclude a release substrate. In one embodiment, the package includes asubstrate with at least one recess with an interior surface. The packageincludes a means for positioning the orthodontic appliance inside therecess such that the composition layer(s) do not separate from theappliance upon removal of the appliance from the recess. Preferably, thepackage further includes a cover for the recess and a means formaintaining the cover in contact with the substrate, wherein the meansfor positioning the orthodontic appliance includes means suspending theappliance in the recess such that the composition layer(s) do notcontact the interior surface of the recess. Such packages are disclosed,for example, in U.S. Pat. No. 5,172,809 (Jacobs et al.).

In another embodiment the orthodontic appliance has a base for bondingthe appliance to a tooth structure and a body extending from the baseand at least two opposed tiewings extending away from the body. The baseand at least one of the tiewings extend past the body in a gingivaldirection and present a gingival recess. The base and at least one otherof the tiewings extend past the body in an occlusal direction andpresent an occlusal recess. The package includes a carrier having a pairof arms extending toward each other. Each of the arms has an outer endsection, with the outer end sections being spaced apart from each otherand presenting a channel therebetween. The orthodontic appliance islocated in the channel and is supported by the arms with one of theouter end sections extending into the occlusal recess and the other ofthe outer end sections extending into the gingival recess. Suchorthodontic appliances and packages are described, for example, in U.S.Pat. No. 6,089,861 (Kelly et al.).

In some embodiments, a packaged article can include a set of orthodonticappliances, wherein at least one of the appliances has a hardenabledental composition of the present invention thereon. Additional examplesof articles and sets of appliances are described in U.S. Pat.Application Publication No. 2005/0133384 A1 (Cinader et al.). Packagedorthodontic appliances are described, for example, in U.S. Pat.Application Publication No. 2003/0196914 A1 (Tzou et al.) and U.S. Pat.Nos. 4,978,007 (Jacobs et al.), 5,015,180 (Randklev), 5,328,363 (Chesteret al.), and 6,183,249 (Brennan et al.).

An orthodontic appliance having a hardenable dental composition of thepresent on the base thereof may be bonded to a tooth structure usingmethods (e.g., direct or indirect bonding methods) that are well knownin the art. Upon application of the orthodontic appliance to the toothstructure, the hardenable dental composition of the present inventioncan be hardened to adhere the orthodontic appliance to the toothstructure. A variety of suitable methods of hardening the compositionare known in the art. For example, in some embodiments the hardenabledental composition can be hardened by exposure to UV or visible light.In other embodiments, the hardenable dental composition can be providedas a multi-part composition that hardens upon combining the two or moreparts.

When desired, typically upon completion of the orthodontic treatmentprocess, the practitioner needs to remove the orthodontic appliance fromthe tooth structure. Hardened dental compositions of the presentinvention are designed to reduce the bond strength upon heating to allowfor convenient removal of not only the orthodontic appliance, but alsofor removal of any hardened dental composition remaining on the toothstructure after removal of the appliance.

The hardened dental composition can be heated by any convenient methodincluding, but not limited to, heating with lasers, warm water,electrothermal debonding units, heated gel tray, as well as othermethods known in the art.

Alternatively, for hardened dental compositions includingradiation-to-heat converters, the hardened dental composition canoptionally be heated by irradiation with radiation that is absorbed bythe radiation-to-heat converter. A wide variety of radiation sources canbe used including, for example, lasers, laser diodes,quartz-tungsten-halogen lamps, mercury lamps, doped mercury lamps,deuterium lamps, plasma arc lamps, LED sources, and other sources knownin the art.

The hardened dental composition can optionally be heated to a convenienttemperature for a time sufficient to decrease the bond strength andallow for convenient removal of the orthodontic appliance from the toothstructure. Preferably the temperature and time are chosen to preventdamage to the tooth structure as described, for example, in Zach et al.in “Endodontics,” Bender, Editor, pp. 515-530 (1965). See, also, Lauferet al., Journal of Biomechanical Engineering, 107:234-239 (1985); Launayet al., Lasers in Surgery and Medicine, 7:473-477 (1987); Azzeh et al.,American Journal of Orthodontics and Dentofacial Orthopedics, 123:79-83(2003); and Uysal et al., Angle Orthodontist, 75:220-225 (2005).Typically, by using heating techniques that rapidly heat the dentalcomposition, higher temperatures can be used for shorter durationswithout damaging the tooth structure.

In certain embodiments, at least a portion, and preferably all, of thehardened dental composition, optionally, is heated to at least 42° C.,sometimes at least 50° C., and other times at least 70° C. Typically,the hardened dental composition is heated to at most 200° C., sometimesat most 150° C., other times to at most 100° C., and even other times toat most 80° C. The selected temperature is maintained for a timesufficient to result in the desired decrease in bond strength. Incertain embodiments, the time is at most 10 minutes, sometimes at most10 seconds, and other times at most 1 second. The decrease in bondstrength typically results in fracture within the hardened compositionlayer.

In some embodiments, the orthodontic appliance includes an additionaldental composition layer. Such additional dental composition layers caninclude, for example, unhardened or hardened dental compositions (e.g.,in certain embodiments, a conventional dental composition not includinga thermally labile component). The inclusion of additional layers caninfluence, for example, where fracture takes place during debonding ofthe orthodontic appliance from the tooth structure, as described hereinbelow.

For example, FIG. 4 illustrates an embodiment in which orthodonticappliance 10 has one additional dental composition layer 24 in contactwith composition layer 22. Composition layer 22 may be either anunhardened or hardened dental composition of the present invention.Additional layer 24 is on composition layer 22 opposite base 12.Additional layer 24 is typically an unhardened dental composition (e.g.,an orthodontic adhesive, an orthodontic primer, or a combinationthereof). Upon application of orthodontic appliance 10 to a toothstructure, additional layer 24 (and composition layer 22 if not alreadyhardened) can be hardened by a variety of methods as described hereinabove to adhere the orthodontic appliance to the tooth structure.

In some embodiments, additional layer 24 can be a hardenable orthodonticprimer that is coated on the tooth structure (and optionally hardened)before the orthodontic appliance with composition layer 22 thereon isadhered to the tooth surface.

Upon completion of the orthodontic treatment, at least a portion ofhardened composition layer 22 can be heated to reduce the bond strength,and preferably allow fracture within heated composition layer 22 uponremoval of the orthodontic appliance. Fracture within heated compositionlayer 22 results in fracture near the orthodontic appliance and awayfrom the tooth structure. Further, the heated, hardened compositionlayer 22 (e.g., an orthodontic adhesive) typically has a lower modulus,and therefore is softer to allow for easier cleanup and/or removal ofany remnants of the hardened composition. Therefore, after orthodontictreatment, one embodiment of FIG. 4 would be where composition layer 22and additional layer 24 are both hardened orthodontic adhesives. Inanother embodiment, composition layer 22 would be a hardened orthodonticadhesive and additional layer 24 would be a hardened orthodontic primer.

FIG. 5 illustrates another embodiment in which orthodontic appliance 10has one additional dental composition layer 20 in contact withcomposition layer 22. Additional layer 20 is between base 12 andcomposition layer 22. Additional layer 20 is typically an unhardened orhardened dental composition (e.g., an orthodontic adhesive, anorthodontic primer, or a combination thereof). Composition layer 22 istypically unhardened. Upon application of orthodontic appliance 10 to atooth structure, composition layer 22 (and additional layer 20 if notalready hardened) can be hardened by a variety of methods as describedherein above to adhere the orthodontic appliance to the tooth structure.

In some embodiments, composition layer 22 can be a hardenableorthodontic primer that is coated on the tooth structure (and optionallyhardened) before the orthodontic appliance with additional layer 20thereon is adhered to the tooth surface.

Upon completion of the orthodontic treatment, at least a portion ofhardened composition layer 22 can be heated to reduce the bond strength,and preferably allow fracture within heated composition layer 22 uponremoval of the orthodontic appliance. Fracture within heated compositionlayer 22 results in fracture near the tooth structure. For embodimentsin which composition layer 22 is an orthodontic primer and additionallayer 20 is an orthodontic adhesive, the hardened orthodontic adhesiveis substantially retained on the removed orthodontic appliance. As usedherein, “substantially retained on the removed orthodontic appliance”means that at least 50% by weight, and preferably at least 75% by weightof the orthodontic adhesive is retained on the removed orthodonticappliance. When the hardened orthodontic adhesive is substantiallyretained on the removed orthodontic appliance, clean up and removal ofany adhesive remaining on the tooth structure is more convenient,because less adhesive remains on the tooth structure. Additionally, anycomposition remaining on the tooth structure is preferably substantiallythe hardened dental composition of the present invention, which canoptionally be heated to soften the composition, and thereby allow foreasier adhesive removal. Therefore, after orthodontic treatment, oneembodiment of FIG. 5 would be where composition layer 22 and additionallayer 20 are both hardened orthodontic adhesives. In another embodiment,composition layer 22 would be a hardened orthodontic primer andadditional layer 20 would be a hardened orthodontic adhesive.

For another example, FIG. 6 illustrates an embodiment in whichorthodontic appliance 10 has two additional dental composition layers(20 and 24) in contact with composition layer 22. Additional layer 20 isbetween base 12 and composition layer 22. Additional layer 20 istypically an unhardened or hardened dental composition (e.g., anorthodontic adhesive, an orthodontic primer, or a combination thereof).Composition layer 22 can be unhardened or hardened. Additional layer 24is on composition layer 22 opposite base 12. Additional layer 24 istypically an unhardened dental composition (e.g., an orthodonticadhesive, an orthodontic primer, or a combination thereof). Uponapplication of orthodontic appliance 10 to a tooth structure, additionallayer 24 (and composition layer 22 and additional layer 20, if notalready hardened) can be hardened by a variety of methods as describedherein above to adhere the orthodontic appliance to the tooth structure.

In some embodiments, additional layer 24 can be a hardenable orthodonticprimer that is coated on the tooth structure (and optionally hardened)before the orthodontic appliance with additional layer 20 andcomposition layer 22 thereon is adhered to the tooth surface.

Upon completion of the orthodontic treatment, at least a portion ofhardened composition layer 22 can be heated to reduce the bond strength,and preferably allow fracture within heated composition layer 22 uponremoval of the orthodontic appliance. Fracture within heated compositionlayer 22 results in fracture between, yet safely away from, theorthodontic appliance and the tooth structure. Therefore, afterorthodontic treatment, one embodiment of FIG. 6 would be wherecomposition layer 22 and additional layers 20 and 24 are all hardenedorthodontic adhesives. In another embodiment, composition layer 22 wouldbe a hardened orthodontic adhesive and additional layers 20 and 24 wouldbe hardened orthodontic primers.

It is to be understood that additional embodiments are contemplated inwhich additional layers or arrangements of layers are present. Further,the thickness of each layer can be individually varied as desired.Further, dental compositions of the present invention need not bepresent only in explicitly defined layers, but can also be presentdistributed uniformly or non-uniformly throughout all or a portion ofthe layer(s) present on the base of the orthodontic appliance.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. Unless otherwiseindicated, all parts and percentages are on a weight basis, all water isdeionized water, and all molecular weights are weight average molecularweight.

EXAMPLES Test Methods

Bond Strength with Glass Rods Test Method

A single drop of adhesive sample was applied to the end of an 8-cm longglass rod and a small amount of 0.254-mm average diameter glass beads(Z-light spheres, Type W-160, 3M Company) were sprinkled on theadhesive. The glass rod was then lightly pressed against a thicker 4-cmlong glass rod and pulled apart to let dry for 10 minutes. The larger ofthe glass rods was held vertically, adhesive side up, in a holder andthe smaller glass rod was balanced vertically on top and the adhesivecured for 30 seconds with a dental halogen lamp (Model 2500, 3M ESPE, 3MCompany). The thickness of the adhesive layer was determined by thethickness of the glass beads used.

A wire attached to an eyelet on the upper glass rod was attached to aMTS Sintech tensile tester (Model #T30/87/100, MTS Systems Corp., EdenPrairie, Minn.) and pulled at a rate of 2.54 mm/minute with an area of12.9 mm² until the adhesive bond between the glass rods assembly wasbroken. (Note that the actual area of TRANSCEND 6000 bracket (Part#59543-01, 3M Unitek, Monrovia, Calif.) is about 12.5 mm².) The force ofbreaking the adhesive bond at various temperatures, including roomtemperature (RT, about 23° C.) was measured in terms of MPa and reportedas an average of 2 or 3 replicates. The Sintech clamps were placed in anoven that allowed heating of the samples.

Bond Failure Time on Teeth Test Method

Orthodontic brackets were bonded to bovine teeth surfaces by aphotocuring procedure as follows: Bovine teeth were prophyed by using anaqueous paste of medium Italian pumice (Servalab, Paramus, N.J.) andsubsequently washed clean with water. The teeth were dried with a streamof dry air and then etched and primed with ADPER PROMPT L-POP selfetching primer (3M ESPE). TRANSCEND 6000 ceramic brackets (Part#59543-01, 3M Unitek, Monrovia, Calif.) were bonded to the etched andprimed teeth with APC Plus orthodontic adhesive (3M Unitek, Monrovia,Calif.) using a Model 2500 dental halogen light source (3M ESPE DentalProducts Division, St. Paul, Minn.).

In Example 7, the procedure for prophying, etching and priming the teethdescribed above was followed by application of a thin coating(0.00254-cm thick) of the polyurethane primer described in Example 7.Victory Series metal brackets (Part #017-401, 3M Unitek) or TRANSCEND6000 ceramic brackets (Part #59543-01, 3M Unitek) were bonded to theprepared teeth with APC PLUS orthodontic adhesive (3M Unitek) using aModel 2500 dental halogen light source (3M ESPE). The controls inExample 7 were bonded without the application of the polyurethaneprimer. Additionally, thermocouples were embedded in the adhesive bondsof the Control samples.

In order to measure bond strength, an Ardel/Kinamatic two-axis linearstage equipped with two Starrett micrometers (2.54-cm travel distance,0.00254-cm step each in the x and y direction) having a 5.08-cm diameteraperture was mounted on a fixed 10.16-cm high platform. Two steel wires(0.0508-cm diameter) were run 0.3 cm apart across the aperture of thetwo-axis stage such that brackets that had already been adhered topotted teeth were secured to the stage by passing the steel wiresthrough the ligature grooves above and below the bracket. A 500-g weightwas hung from the bottom of the potted tooth by means of a hook screwedinto the potting material such that the weight provided a constant 500-gforce (by gravity) to pull the tooth away from the bracket. The tip of a120V hot solder iron estimated to be 177° C. was then touched to thebracket until the adhesive bond failed and the time to failure wasrecorded as an average of 3 replications.

Abbreviations, Descriptions, and Sources of Materials

Abbreviation Description and Source of Material HEMA 2-Hydroxyethylmethacrylate (Sigma-Aldrich, St. Louis, MO) TERATHANE 650Polytetramethylene ether diol (Invista, Wichita, KS) H12 MDIBis-(4-isocyanatocyclohexyl) methane or DESMODUR W (Bayer, Pittsburgh,PA) VORANOL 225 Triol compound (Dow Chemical, Midland, MI)

Example 1 Preparation of OX-1 DMA

The compound OX-1 DMA (Example 1) was prepared by the synthetic routedetailed in Example 2 of U.S. Pat. No. 6,652,970 (Everaerts et al).

Example 2 Preparation of DIOL-10

A solution consisting of 22.1 gm of1,1-(4,4′-methylenebiphenylene)bismaleimide (Sigma-Aldrich) and 48 gm offurfuryl alcohol (Sigma-Aldrich) was prepared in 150-200 ml of methylenechloride. The solution was refluxed overnight and then allowed to coolto room temperature. Enough diethyl ether was added to the productmixture to precipitate out the product. The precipitate was collected byvacuum filtration, redissolved in methylene chloride and reprecipitatedin diethyl ether for an additional 1-2 times to purify it some more.Finally the precipitated material was collected by vacuum filtration,dried under vacuum and then allowed to further air-dry overnight. Theidentity of product DIOL-10 (Example 2) was confirmed by NMRspectroscopy.

Example 3 Preparation of DIOL-10 DMA

The compound DIOL-10 DMA (Example 3) was prepared by the syntheticprocedure of Example 2, except that furfuryl methacrylate(Sigma-Aldrich) was used instead of furfuryl alcohol.

Examples 4A-B and 5A-B Adhesive Compositions Containing a ThermallyLabile Di(meth)acrylate Compound

Adhesive compositions containing thermally labile dimethacrylatecompounds at various weight % concentrations were prepared by handstirring Example 3 (Compound DIOL-10 DMA) into ADPER Single BondAdhesive (ASBA; 3M Company) to provide Example 4A (33 weight %) andExample 4B (66 weight %); and by hand stirring Example 1 (Compound OX-1DMA) into ASBA to provide Example 5A (33 weight %) and Example 5B (66weight %).

Example 6 Primer Composition Containing a Thermally LabileDimethacrylate Compound

A primer composition containing a thermally labile dimethacrylatecompound was prepared by stirring Example 3 (Compound DIOL-10 DMA) intoHEMA at 25 weight % to provide Example 6.

Bond Strength Evaluations of Examples 4A-B, 5A-B, and 6 Examples 4A-Band 5A-B were individually dissolved in ethyl acetate (65 weight %) andevaluated for bond strength (between 2 glass rods) according to the BondStrength with Glass Rods Test Method described herein. Additionally,Example 6 (DIOL-10 DMA in HEMA) was evaluated as primer according to theBond Strength with Glass Rods Test Method described herein, except thatthe Example 6 primer was applied to the upper glass rod as a single drop(approximately 10 mg) that was blown to a thin film with a stream of dryair before the application of ASBA (no additive). The results areprovided in Table 1 and are compared with the bond strength of ASBAcontaining no additive (Control).

TABLE 1 Bond Strengths (MPa) at Various Temperatures Ex- ThermallyLabile ample Compound (Weight %) RT 70° C. 99° C. 126° C. 4A DIOL-10 DMA(33) in 6.49 3.13 4.23 0.50 ASBA 4B DIOL-10 DMA (66) in 5.59 2.14  NT*0.04 ASBA 5A OX-1 DMA (33) in 8.88 NT NT 0.17 ASBA 5B OX-1 DMA (66) in3.53 NT NT 0.03 ASBA 6 DIOL-10 DMA (25) in 13.98 3.93 NT 0.03 HEMA ASBANone 10.10 7.95 3.61 3.75 *NT—Not Tested

The data in Table 1 show that heat alone (ASBA; Control Sample) had someeffect on reducing the bond strength between the two glass rods, howeverthe bond strength was reduced much more significantly with the presenceof either DIOL-10 DMA or OX-1 DMA thermally labile compounds and seemedto correlate with the concentration of compound in the adhesive, i.e.,the higher the compound concentration, the lower the bond strength. Bondstrengths were very low for the thermally labile compound-containingadhesives at the highest tested temperature of 126° C. In the case ofExample 6 (DIOL-10 DMA/HEMA applied as a primer followed by theapplication of ASBA), the primer significantly increased theroom-temperature (RT) bond strength, and again the bond strengthdecreased dramatically with increasing temperatures with a very low bondstrength recorded at 126° C.

These evaluations demonstrate that the incorporation of thermally labiledi(meth)acrylates into hardened dental compositions can providesignificantly lower bond strengths when the bonded materials are heated.

Example 7 Primer Composition Containing a Thermally Labile Diol Compound

A primer composition (Example 7) containing a thermally labile diolcompound was prepared by combining Example 2 (DIOL-10) with the otheringredients as shown in Table 2. A typical procedure involved heating7.0 gm of H12MDI and 8.0 gm of TERATHANE 650 in 28 gm of THF with 1 dropof dibutyltin dilaurate (Sigma-Aldrich) for 1.25-8 hours using an IRlamp with constant stirring. Subsequently, 7.4 gm of DIOL-10 in 22.3 gmof THF and 0.49 gm of VORANOL 225 was added and the mixture was stirredovernight at ambient temperature. The excess isocyanate was quenchedusing N,N-bis(3-aminopropyl)methylamine with FT-IR monitoring of thedisappearance of the isocyanate absorption band around 2270 cm⁻¹. Theresulting polyurethane was then placed in a 60° C. oven overnight toremove all the THF solvent. The resulting composition was used as theprimer in Example 7 as detailed in the Bond Failure Time on Teeth TestMethod.

TABLE 2 Ingredients used to prepare Example 7 Polyurethane PrimerComposition Ingredient Weight Percent (%) DIOL-10 23.3 TERATHANE 65034.9 H12 MDI 35.3 VORANOL 225 6.5

Bond Strength Evaluations Utilizing Example 7 Primer

Example 7 was utilized as a primer followed by application of APC PLUSorthodontic adhesive (3M Unitek) and evaluated for bond strength(between an orthodontic bracket and bovine teeth) according to the BondFailure Time on Teeth Test Method described herein. The results areprovided in Table 3 and are compared with the bond strength of APC PLUSorthodontic adhesive (without the Example 7 primer) between a bovinetooth surface and metal and ceramic brackets (Control Samples).

TABLE 3 Time to Failure of Bracket-to-Tooth Adhesive Bonds Failure RunPrimer Bracket Temp Time (Seconds) 1 Example 7 Metal About 160° C. 5Control None Metal 160° C. 120 Control None Ceramic 135° C. 60

The data in Table 3 show that time for debonding at elevated temperaturewas significantly reduced by using a polyurethane primer containing athermally labile diol. Additionally, it was observed that the adhesivebond failed at the tooth-adhesive interface as contrasted to the morecommonly observed bracket-adhesive interface.

Example 7 was also evaluated for bond strength (between an orthodonticbracket and bovine teeth) according to the Bond Failure Time on TeethTest Method described herein, except that a CO₂ laser operating at 10.6μm (Diamond 84 CO₂ Laser with the Performance Package, Coherent Inc.,Santa Clara, Calif.) replaced the solder iron as a heat source. Sincethe laser heated up extremely fast, the watts and seconds pulsed wererecorded and the results were as follows:

Laser at 10 watts and Control: remained bonded 4 seconds Example 7: bondfailed at tooth-adhesive interface Laser at 15 watts and Control: bondfailed at bracket-adhesive interface 2 seconds Example 7: bond failed attooth-adhesive interface

These results are again consistent with the utility of using a thermallydegradable layer for controlling the debonding and location of bracketremoval from a tooth surface.

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

1. An article comprising: an orthodontic appliance having a base forbonding the appliance to a tooth structure, a body extending outwardlyfrom the base, and an archwire slot; and a hardenable dental compositionon the base of the appliance, wherein the hardenable dental compositioncomprises a hardenable component having bonded thereto one or morethermally labile groups selected from the group consisting ofcycloaddition adducts, oxime carboxylate esters, and combinationsthereof; and an initiator for initiating hardening of the hardenabledental composition, wherein the one or more thermally labile groups arebonded to the hardenable component after hardening.
 2. An articlecomprising: an orthodontic appliance having a base for bonding theappliance to a tooth structure; and a hardenable dental composition onthe base of the appliance, wherein the hardenable dental compositioncomprises a hardenable component having bonded thereto one or morethermally labile groups; and an initiator for initiating hardening ofthe hardenable dental composition, wherein the hardenable componentcomprising the one or more thermally labile groups is selected from thegroup consisting of: compounds represented by the formula (Formula I):

wherein R¹ is hydrogen or an organic group; R² and R³ each independentlyrepresent an organic group; each E¹ and E² independently represents anethylenically unsaturated group; m and n are each independently 0 or 1;and R³ and E² can optionally be combined to form one or more ringsand/or two or more groups among R¹, R², and E¹ can optionally becombined to form one or more rings; compounds represented by the formula(Formula II):

wherein R⁴ and R⁵ each independently represent an organic group; Drepresents a cycloaddition adduct; each E³ and E⁴ independentlyrepresents an ethylenically unsaturated group; o and p are eachindependently 0 or 1; and two or more of R⁴, R⁵, E³, E⁴, and/or D canoptionally be combined to form one or more rings, with the proviso thatthe one or more rings do not interfere with the thermal lability of D;and combinations thereof, wherein the one or more thermally labilegroups are bonded to the hardenable component after hardening.
 3. Anarticle comprising: an orthodontic appliance having a base for bondingthe appliance to a tooth structure; and a hardened dental composition onthe base of the appliance, wherein the hardened dental compositioncomprises a thermally labile component having bonded thereto one or morethermally labile groups selected from the group consisting ofcycloaddition adducts, oxime carboxylate esters, and combinationsthereof, wherein the bond strength of the hardened dental composition atan elevated temperature decreases compared to the bond strength of thehardened dental composition not including the thermally labile componentat the same elevated temperature, wherein the elevated temperature is atleast 42° C. and no greater than 200° C.
 4. The article of claim 3wherein the article further comprises one or more additional layers ofdifferent hardenable and/or hardened dental compositions.
 5. The articleof claim 1 wherein the oxime carboxylate esters are oximenon-halogenated-carboxylate esters.
 6. The article of claim 3 whereinthe oxime carboxylate esters are oxime non-halogenated-carboxylateesters.
 7. The article of claim 3, wherein the storage modulus of thehardened dental composition at an elevated temperature decreasescompared to the storage modulus of the hardened dental composition notincluding the thermally labile component at the same elevatedtemperature.
 8. The article of claim 7, wherein the storage modulus ofthe hardened dental composition at the elevated temperature is nogreater than 60% of the storage modulus of the hardened dentalcomposition not including the thermally labile component at the sameelevated temperature.
 9. The article of claim 3, wherein the bondstrength of the dental composition at the elevated temperature is nogreater than 90% of the bond strength of the hardened dental compositionnot including the thermally labile component at the same elevatedtemperature.